How to Engineer Viral Social Proof by@hojung

How to Engineer Viral Social Proof

The right rewards build the foundation for any rewards campaign. Tyler Denk, a growth engineer from Morning Brew, explains how their rewards helped them build an audience of 1.5 million subscribers. Don’t be afraid to spend time on this first step. Figure out what makes your product or service special, and build your campaign around that unique offering. For Morning Brew that included a Premium Sunday newsletter, access to Exclusive Community perks, and a fabled trip to their HQ in New York City for referrers.
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Hojung Kim

Chief Gathering Officer @ gathr, a

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Disclosure: We use Viral Loops, Webflow and Proof and are part of their affiliate programs. Clicking the links on this page will help us continue purchasing their services.

Our pivot from a B2B real estate services startup into a supercharged social events app was an utter whirlwind. The pivot changed our tech stack from top to bottom, shifted our team’s roles and skill requirements, and upheaved our entire market.

That was already enough to throw us into an existential panic. But on top of it, we lost our entire userbase. We were no longer selling to large apartment buildings as a real-estate tech play, we were trying to get a consumer app out the door. And customer lead gen was about to get a lot harder.

The B2B sales process is simple enough: pick up the phone and call leads. Move them through CRM pipelines. (Hopefully) watch the digits go up in the bank. Repeat.

But building a consumer app userbase?

We were pretty lost.

Even worse, we made a complete pivot, so we were months away from even having a usable product. How were we supposed to generate a userbase when we didn’t even have anything sell?

We searched and searched to no avail. It seemed that there was no template for building a consumer userbase because, well, there really isn’t one. Each consumer business is its own unique and complex contraption. That’s what makes them simultaneously exhilarating and maddening, like a startup version of Schrödinger’s cat.

That’s why consumer startup founders rarely hit more than one home run, while B2B founders often repeat their way through the lead gen, prospect, and sell cycle to multiple crisp base runners. Consumer apps just don’t have a single replicable template.

However, we did know that we could start from these two first principles. Users would always respond to:

The right incentives — rewards or prizes to incentivize user actions.Social proof — following others taking the same actions.

As long as we built around those two things, we could start marketing campaigns even without a full product up and running. Furthermore, if our campaign’s traffic grew over time, it would give us the confidence to keep building knowing that we were at least moving in something close to the right direction.

That’s how we decided to build a viral social proof campaign with the help of two tools: Viral Loops and Proof. We’re still figuring out if it’ll work for us in the long-run, but the early returns (+1400% site traffic in the first week) are pretty encouraging.

Since it worked for us, we decided to build a brief guidebook to let anyone do the exact same for their startup. So without further ado, here’s how to build a viral social proof campaign in 4 simple steps.

Step 1: Build a Rewards Campaign

The right rewards build the foundation for any rewards campaign. Here’s Tyler Denk, a growth engineer from Morning Brew, explaining how their rewards helped them build an audience of 1.5 million subscribers.


Don’t be afraid to spend time on this first step. Figure out what makes your product or service special, and build your campaign around that unique offering. For Morning Brew, that included a Premium Sunday newsletter, access to Exclusive Community perks, and a fabled trip to their HQ in New York City for super-ultra referrers. On top of that, all of their swag features their distinctive branding front and center, key for a newsletter that relies on brand awareness and viewership.

The prizes don’t have to be physical if your startup is cash-constrained. Over at gathr, a for organizing social events, we built out our campaign by creating pre-launch tiers for our app. We decided to grant early access to users at certain dates based on their ranking in our referral campaign. Our top 100 referrers would get access by March 1st, our top 1,000 by April 1st, etc.


The key here is to build out rewards that work in line with your product. And the product itself has to already be good enough that word-of-mouth referrals are happening even before you implement a formalized referral program. As Denk mentions in an article he wrote for Medium’s Mission publication:

“Trying to optimize a referral program for an incomplete (or useless) product is the equivalent of trying to fill a bucket with a hole in the bottom. Analogy ✓.”

Here are a few of the best referral programs we’ve seen to date.

Harry’s doled out free product before they were even ready to ship itDropbox gave out up to 16 GB of free storage, with 500 MB for each friend referredHQ Trivia gave out extra lives when users invited their friends to playMailbox generated a waitlist of 380,000 users by awarding earlier access to users who referred more friends

While it isn’t a requirement of successful companies, the right referral campaign can be a major deciding factor in your startup’s growth.

Step 2: Install Viral Loops


Viral Loops is an out-of-the-box referral marketing tool that lets you build rewards campaigns without having to write a single line of code. After signing up for a 14-day free trial, follow their step-by-step process to quickly get up and running.

Viral Loops uses tried and true templates for referral marketing based on campaigns run by successful startups. Let’s say you want to build a pre-launch waiting list before your product’s ready to go out the door, like us. You can take advantage of The Startup Prelaunch template that Robinhood used to get 1 million users before they even launched.


If you’re not sure which template is best for you, the Viral Loops blog has a ton of useful advice. They even provide an entire handbook on referral marketing, as well as a number of actionable case studies that informed their templates. Those studies include Robinhood’s incredible pre-launch as well as other successful campaigns like Harry’s razors getting 100,000 emails in a single week or Dropbox’s 3900% growth.

Create Campaign

After signing up, hit the big red Create Campaign button to get started. After you do, you’ll hit a page where Viral Loops will recommend specific campaign templates based on your use case.


If you want to ignore their recommendations and just see all your options, click All templates in the top left corner next to Recommended. Switch back to Recommended if you want to go back to using their suggestions.

For the following walkthrough example, we’re going to use the general rewards program that fueled Dropbox’s growth with our new software recommendation blog, Scale Combo. Scale Combo seeks to empower entrepreneurs with software combo recommendations to help them move faster, aim higher, and build better companies using the right resources. It’s pretty much all the things we wish we knew back in January 2018 when we first started as entrepreneurs. If we had, we would have saved months if not years of time.

Viral Loops and Proof are both a core part of our marketing stack and are also the first Scale Combo we’re recommending to entrepreneurs.


You can use your own existing website for the referral campaign, but Viral Loops also offers its own landing page builder if you don’t already have one. Since we’re just launching Scale Combo, we’re going to use Viral Loops pages.

Next up is everyone’s favorite part — adding in the actual rewards. As mentioned above, if you’re pretty cash-constrained, you can choose rewards that work directly with the product you’re already building. For Dropbox, that led to a 2-sided referral campaign where the referrer and invitee both received 500 MB of free storage up to 16GB.


For Scale Combo, we decided to offer different rewards on the invitee and referrer side. We’re giving free Scale Combo stickers to all invitees. In addition, we’re taking a page out of Dropbox’s book and offering a free 3 months of a premium subscription to all referrers.

This kind of referral program is known as a two-sided referral program. By incentivizing both the referrer and the invitee, it promotes a continuous flow of referrals from Day 1 to Launch.

Next, you’ll have the option to customize your widgets, notifications, and integrations, but we’ll skip over those for now. How you personalize those to fit your campaign is entirely up to you and how you want to build your brand.


If you want to use Viral Loops’ own pages, this step is already done! But if you want to use your own website builder, Viral Loops offers easy installation instructions for the following website builders:

Personally, we recommend using Webflow, a no-code website builder that offers customizable design capabilities second to none. Even if you already know how to code, Webflow offers a best-in-class designer that designers, developers, and laymen like me can easily navigate with the help of Webflow University. (Webflow University also doubles as a perfect way to get into design and front-end web development, and actually served as my first introduction to software development.) Unfortunately, because it’s still new, Webflow isn’t one of Viral Loops’ supported website builders.

Lucky for you, we went through the semi-wayward process of installing Viral Loops on Webflow, so we’re attaching our own guide here.

Webflow Installation


Go to the Settings tab in your Webflow dashboard, then click Custom Code. From here, scroll down to Footer Code. This section can be a bit tricky to find because Viral Loops tells you to look for </body> tags. Webflow heads this section with Footer, with a much smaller subheading reading “Add code before </body> tag.”


After copying the Viral Loops code in, hit Save Changes and Publish and you’re all done!

Step 3: Install Proof

Once you’ve installed Viral Loops, you’re already well on your way to building a traffic engine for your startup. The next piece of the puzzle is to create social proof around signing up. Simply installing Proof can increase your sign-ups by as much 46%, which together with Viral Loops can turbocharge your referral campaigns.


Proof is a simple pixel that you can install on your site to increase sign-ups by an average of 10%. Check out their website to see it in action, but it allows you to showcase other people signing up for your campaign in real-time. This type of social proof is a major (trigger, but synonym cause I don’t want to confuse people with Zap trigger overlapping words) pushing people to complete actions on your site. Like Viral Loops, it comes with a 14-day free trial to make sure it’s the right move for you.

Gustav Alstromer, Airbnb’s former Head of Growth and current Y Combinator partner, puts it best:

“Adding live social proof was the #1 driver of increased revenue in all my experiements while at Airbnb.”

Even if it would only increase sign-ups by only 10%, Proof was a no-brainer for us because of compound growth. This holds true across all referral rates with Viral Loops.

“Compound interest is the 8th wonder of the world.” — Albert Einstein

While Proof served us as an add-on to Viral Loops, it’s perfectly reasonable to use it as a stand-alone product, too. The following walkthrough assumes that you’ll install it in tandem with Viral Loops, but that isn’t necessary and can be done with the same steps.


First, Proof asks you to add a bit of code to your site header. Most website builders will have a place for that called a Custom Code section.


We’ll walk through what that looks like on our Webflow site, but check your website builder’s help docs to find where it’s at on your own site.

The relevant Webflow section is in Settings, then Custom Code like before, but this time, we’re looking for Head Code.


Copy and paste the Proof pixel, hit Save Changes, then Publish! You’re done, and you should see the following success message if you navigate back to Proof’s setup.


Congrats! You’re ready to move on to the fun part — actually designing your campaign.

Design Campaign Goals

Proof lets you customize your pixel in line with your campaign goals. For the first step, Creating your Goal, you’ll just pick whatever your campaign's objective is.


On Scale Combo, for example, we might select Subscribe as our goal category, name our goal Sign Up, and set a conversion value of $20 if we believe that 20% of all subscribers will go on to purchase Scale Combo Premium at an Life-Time Value (LTV) of $100. While the conversion value primarily applies to Software-as-a-Service (Saas) or other online purchase startups, it also serves as a useful way to track LTV and compare it to your Customer Acquisition Costs (CAC) over time. (If you need more info on any of these terms, scroll to the Appendix for definitions of all the terminology used throughout the article.)

Design Campaign

Proof offers a bunch of different customizations beyond the scope of a single article, but we’ll primarily focus on their variant functionality. This allows you to A/B test different versions of the Proof pixel to maximize potential traffic conversion.


You’ll see that you can disable Proof Notifications for a percentage of website visitors under Traffic Holdback (enabled by default at 5%). Enabling this will allow you to show your Proof pixel variant to 95% of website visitors while using the remaining 5% as a control.

You can then see how much Proof is affecting traffic conversion rates based on different variants. On our end, we eventually settled on a version that increased conversion by 21.19%.


For Steps 3 and 4, Capturing Data and Displaying on Site, choose Zapier and your main landing page. If you prefer to use Proof alone rather than in tandem with Viral Loops, simply choose Auto in Step 3.

Step 4: Integrate Viral Loops and Proof with Zapier

If you’re not already familiar with Zapier, it’s a lightning-fast way to automate and pass information between all of your apps and workflows. It’s the foundation of most of the various tool stacks that we recommend over at Scale Combo.

You’ll need to sign up for Zapier before this final step, so make sure to get that ready first. Once you do, click on the Make a Zap! button to get started

1. When this happens…

Choose Viral Loops as your first app. Under trigger event, there should only be one option — New Participant. That’s the option we want!


Continue on to…

2. Do this …

Choose Proof as your action app, and choose Create Conversion as your Action Event.


3. …


That’s it! There’s no Step 3! You’re ready to go, so just turn your Zap on and you’ve completed the marketing stack!

Some final words:

While Viral Loops and Proof together offer an amazing marketing stack, no marketing will solve a lack of product-market fit. We quoted Denk, growth specialist at Morning Brew, earlier in the article and his analogy remains true. Marketing a product without product-market fit is analogous to filling a bucket with a hole at the bottom — you’ll just end up flooding the room and putting yourselves underwater.

On the other hand, marketing with the right feedback indicators can actually guide your startup’s trajectory toward product-market fit. That’ll be our next article, so stay tuned for A Marketing Analytics Stack to Engineer Product-Market Fit.

Appendix: A List of Vocab Words from the Article

Vocab listed in order of appearance in the article:

  • Virality — The tendency of a piece of information to be rapidly circulated, mostly referring to the Internet.
  • Social Proof — A psychological and social phenomenon where people copy actions undertaken by others.
  • Rewards Campaign — Also known as a referral campaign, a rewards campaign is a marketing strategy where companies provide incentives for users who complete specific actions.
  • Invitee — The one who gets referred in a referral campaign.
  • Referrer — The referring agent in a referral campaign. 
  • Two-Sided Referrals — Referral campaigns that incentivize both the invitee and referrer with prizes to sign-up. Creating two-sided referral programs can 
  • Footer Code — Webflow’s section for custom code to be placed within the </body> tags. You can find it by navigating to Custom Code in the Settings of your Webflow site’s dashboard.
  • Compound Growth — A measure that determines an exponential growth rate over a specific time period.
  • Referral Rate — The rate at which a referrer refers other users over a specific time period.
  • Custom Code — A section that website builders usually reserve for installing pixels, tools, or other external software. This is usually equivalent to the block of code within the </head> tags in HTML.
  • Subscribe — An action undertaken to receive something at regular intervals.
  • Life-Time Value (LTV) — The amount of revenue a company can expect to receive from a single user. Commonly used in tandem with average LTV to measure across all users in a userbase or user cohort.
  • Software-as-a-Service (SaaS) — A software distribution model in which users pay a rate to subscribe and utilize a product or service, often over the Internet.
  • Customer Acquisition Cost (CAC) The amount a company can expect to expense to acquire a single user. Commonly used in tandem with average CAC to measure across all users in a userbase or user cohort.
  • Variant —Referencing different versions used to conduct an A/B test. 
  • A/B Test — Originally a statistical analysis term, startups have adopted it to refer to adjusting different features or variables to optimize conversion rates.
  • Conversion Rate — The percentage of users that successfully complete a given action.
  • Control— The variant of the A/B test that is kept constant, or without changing the original version. (Also referred to as the A version in an A/B.)
  • Zap — Zapier’s name for the automated triggers it enables between different apps and workflows.
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