Thanks to a $64.2 million acquisition last year, Snap also owns the one iPhone app that's ranked higher: Bitmoji.
Taking a page out of Facebook founder Mark Zuckerberg's M&A playbook, Snap CEO Evan Spiegel is closely tracking where users are spending their time when not on Snapchat, and he's making sure his company doesn't lose out on consumer attention as it plows full speed towards the public markets.
Ironically, Facebook at one point seriously considered investing in the company that makes Bitmoji, and its first product was a customizable comic strip app that went viral on Facebook. For Mark Zuckerberg, Bitmoji may turn out to be the one that got away.
Bitmoji is a free app that lets users personalize emojis and share them with friends through text messages, Facebook Messenger and even on Slack. The service is owned by Bitstrips, a Toronto-based company that's spent the past decade working in the niche business of online customizable comics.
In its IPO prospectus, Snap categorizes Bitmoji as one of its several creative tools that let users "express themselves through Snaps." The company said that over 60 percent of Snaps every day are enhanced through Bitmojis or tools like geofilters and lenses.
"Entertainment is the whole game for them," said Scott Denne, an analyst at 451 Research in New York. "They're betting that as long as people continue to be entertained and engaged that per user revenue will continue going up."
In the fourth quarter, Snap's average revenue per user (ARPU) more than tripled to $1.05, from 31 cents the prior year. Advertisers are starting to move from the experimentation phase with Snapchat to baking it into their marketing budget.
That's critical because when you're already serving 158 million users a day, user growth becomes a challenge. Snap's user base grew 46 percent in December from the prior year, slowing from 48 percent at the same time in 2015 and 92 percent a year before that. So the only way to keep revenue growing as user growth slows is to earn more money from each user.
In addition to facing the law of large numbers, Snap has some stiff competition. Facebook's Instagram and WhatsApp offerings (which cost Zuckerberg a combined $20 billion) are building competitive features to Snap, while other social media and messaging services ranging from Twitter and YouTube in the U.S. to Kakao, Line and WeChat in Asia are vying for eyeballs.
When it gobbled up Bitstrips, Snap picked up a team of app developers who are quite familiar with Facebook.
Bitstrips co-founder and CEO Jacob Blackstock, who goes by B.A., was leading the company when Facebook picked it as a finalist for its incubator, called fbFund, in 2009. (Bitstrips did not end up receiving any investment.)
Up to that point, the company was focused on the education market -- a product called Bitstrips for Schools -- letting kids in Ontario create avatars that would grow with them through the years.
"It was a really powerful product but it was hard to make a big business out of it," said Robert Balahura, a longtime tech entrepreneur in Toronto and adviser to Bitstrips. "Schools don't make a lot of money."
The fbFund was supporting Facebook's effort to lure app developers to its platform, so the many millions (now 1.2 billion) of people on the social network every day would have more to do.
It took a few years after for Bitstrips to launch on Facebook, but it went viral pretty quickly after that. From its introduction in December 2012 until July 2013, 10 million people created avatars, Bitstrips said.
"It got so wildly popular that they had problems keeping up with the server load," said Balahura. "They spent a lot of time fixing that."
And then came the ridicule. BuzzFeed found the comics so spammy that in October it published a post titled, "How To block Bitstrips from Your Facebook timeline."
When Bitstrips raised $3 million in December 2013 from Li Ka-shing's Horizons Ventures, tech news site Virtuaniz called it "the hated Facebook spam."
Investors weren't deterred. In late 2014, Horizons joined up with Kleiner Perkins Caufield & Byers in an $8 million fundraising round and launched a standalone Bitmoji app on the iPhone.
Just as Facebook gave Bitstrips a place to live on the web, the social network gave similar life to Bitmoji. Only in a very different form.
This time it was Facebook's messaging app.
Bitmoji shot into the top 35 iPhone apps in March 2015 after launching on Facebook Messenger, enabling users to add their cartoon selves in messages to friends and family members.
Brands wanted to get in on the act.
Pixar partnered with Bitmoji to release emojis for the computer-animated movie "Inside Out."
Steve Madden added branded shoes to the app, and retailers Foot Locker and Forever 21 established virtual catalogs.
When Snap made its move for Bitmoji last March, the app wasn't yet available to Snapchat users. But it was popular enough on other platforms that the potential was obvious, at least to Spiegel. After all, Snapchat is inherently about sharing pictures and images and is geared toward a younger demographic.
"Without having a killer application, Bitmoji just existed as a novelty and Facebook wasn't a killer platform for it," said Brian Solis, an analyst covering social media at Altimeter Group. "Snap is a better fit."
Four months after the deal, Snapchat users could add Bitmojis to their chats. The app instantly jumped from hovering between the top 50 and 100 on the iPhone to the top five on iOS and top 10 on Google Play, according to App Annie.
For the time being, it's showing staying power. Since Jan. 11, Bitmoji has held the top spot on the iPhone, just ahead of Snapchat, App Annie data shows.
That's at least one trend that has to concern Zuckerberg, even though Facebook is many times the size of Snap. Facebook's own apps are ranked third (Instagram), fifth (Facebook Messenger), eighth (Facebook) and 16th (WhatsApp).