Snapchat's custom emoji creator is now the fastest-growing app in the US

Bitmoji, the personalized emoji app owned by Snapchat, is the fastest-growing app in the United States.

That's according to measurement and analytics firm ComScore, which ranked the top 11 fast-growing apps from December 2014 to December 2016, though it only measured Bitmoji's growth since February 2015.

ComScore found that, in terms of unique visitors over 18, Bitmoji's growth has skyrocketed in the last two years: Bitmoji is up 5,210% since 2015.

Bitmoji's rapid growth isn't totally surprising, since the app is consistently among the top 10 free apps in both the Apple App Store and Google Play Store and it only dropped from No. 1 to No. 2 in Apple's top free apps chart.

Bitstrips - Bitmoji's parent company - was purchased by Snapchat in March 2016 for more than $100 million. Bitstrips started as a way to make personalized comics back in 2007, but then pivoted to creating cartoon avatars in addition to the full comic strips. The Bitmoji app allows users to customize an emoji that looks like them and respond with it in messages.

Snapchat officially integrated Bitmoji into its own app in July, letting users link the Bitmoji app to their Snapchat account and send personalized Bitmojis to friends in chat or place them on top of messages like Snapchat's other stickers and standard emojis.

Bitmoji also expanded beyond mobile in February, adding a Chrome extension that allows users to send Bitmoji in emails, paste them in Google Docs, and more.