When you've designed an app to appeal to shy people, it only seems appropriate to skip the marketing.

That's why James Sun, the cofounder of Anomo, is keeping his app under the radar for now. At least as much as possible.

Anomo is an app that launched in February for iPhone and Android as a location-based dating app. But Sun recently found a whole new audience and pivoted the service into a social network for introverts, as counter-intuitive as that sounds. Unlike some of its competitors like Whisper, it's not fully anonymous, but shy users can mask themselves with avatars. Though its user base is still small — 40,000 downloads, 4,500 daily active users — it's growing by 500% each month.

Those are the kinds of figures even an introvert like Sun can crow about. It puts Anomo on the same playing field as Facebook: According to Sun, users open the app 18 times a day on average, as opposed to 14 times for Facebook. And nearly all of those users are from a demographic Mark Zuckerberg is eager to win back: teens.

The idea behind Anomo is simple enough. Select an avatar and tell the app your gender and age range (95% of daily active users are between 15 and 20). You can choose to verify your age via Facebook, which is handled on the back end; other users can't see your Facebook profile, but they do see your verification. About 65% of Anomo's users are already verified.

"The innovation here is not that you're anonymous," said Sun, below, who is known on the service as White Panda. "It's that you're wearing a mask."

Once suitably masked, you're placed into a mixed-gender group with four other users for a very casual ice breaker, a simple survey in which everyone's answers are revealed at the same time. Anomo takes note of your answers, and the next time you play, it tries to match you with users who answered in similar ways.

At first, Sun and his cofounder Ben Liu conceptualized Anomo as a dating app for the painfully shy, solving a problem they experienced growing up themselves. "We found it hard to meet new people because we're science-oriented kids," Sun said. "We came to the conclusion that we had social anxiety."

However, it turned out there was a need for more than just masked speed dating for the socially anxious. Anomo found a community fleeing Facebook and seeking somewhere to hang out. The startup tapped psychologists to analyze the 2 million questions from the ice breaker answered so far and found that roughly 85% of its users were introverted.

See also: How Introverts Can Stand Out at Work

Sun believes that a large unserved portion of the teen market can be described as "pent-up introverts." These are users who would rather post pictures of tattoos or pieces of artwork than selfies.

Sun said the company is closing on a $1 million round of funding after raising an initial round of $400,000 in the first half of 2013.

According to user polls, the majority of users came to Anomo "to keep their privacy until they meet someone cool," Sun said. "They want to keep their Facebook friends apart from their new friends."

The prevailing wisdom online is that if you offer users any kind of anonymity, even the masked kind, they will default to their worst behaviors. For this reason, YouTube changed its commenting system, requiring connection to a Google+ account.

Sun said he feared the service would be brought down by trolls, but he has only seen three complaints out of four million posts on the app's main message board so far. Each of the offending posts attracted hundreds of complaints, proving that a community of introverts can police itself.

Anomo's proudest moment, according to Sun, came when one user wrote on the main message board that he was contemplating suicide. Immediately, the post received 600 replies, all encouraging the poster to rethink his decision. Overwhelmed by the response, the troubled teen declared he would hang in there.

The fact that Anomo's introverted users tend to gather around one large message board may seem counterintuitive. This may not stay the same as Anomo grows, but for now, it stands as vindication for the notion that shy introverts can be just as social as anyone else. They just need the right kinds of masks.

Image: iStockphoto, 79govinda; Anomo