The Yik Yak app is free. Like many tech start-ups, the company, based in Atlanta, doesn’t generate any revenue. Attracting advertisers could pose a challenge, given the nature of some of the app’s content. For now, though, Mr. Droll and Mr. Buffington are focused on extending Yik Yak’s reach by expanding overseas and moving beyond the college market, much as Facebook did.

Yik Yak’s popularity among college students is part of a broader reaction against more traditional social media sites like Facebook, which can encourage public posturing at the expense of honesty and authenticity.

“Share your thoughts with people around you while keeping your privacy,” Yik Yak’s home page says. It is an attractive concept to a generation of smartphone users who grew up in an era of social media — and are thus inclined to share — but who have also been warned repeatedly about the permanence of their digital footprint.

In a sense, Yik Yak is a descendant of JuicyCampus, an anonymous online college message board that enjoyed a brief period of popularity several years ago. Matt Ivester, who founded JuicyCampus in 2007 and shut it in 2009 after it became a hotbed of gossip and cruelty, is skeptical of the claim that Yik Yak does much more than allow college students to say whatever they want, publicly and with impunity. “You can pretend that it is serving an important role on college campuses, but you can’t pretend that it’s not upsetting a lot of people and doing a lot of damage,” he said. “When I started JuicyCampus, cyberbullying wasn’t even a word in our vernacular. But these guys should know better.”

Yik Yak’s founders say the app’s overnight success left them unprepared for some of the problems that have arisen since its introduction. In response to complaints, they have made some changes to their product, for instance, adding filters to prevent full names from being posted. Certain keywords, like “Jewish,” or “bomb,” prompt this message: “Pump the brakes, this yak may contain threatening language. Now it’s probably nothing and you’re probably an awesome person but just know that Yik Yak and law enforcement take threats seriously. So you tell us, is this yak cool to post?”

In cases involving threats of mass violence, Yik Yak has cooperated with authorities. Most recently, in November, local police traced the source of a yak — “I’m gonna [gun emoji] the school at 12:15 p.m. today” — to a dorm room at Michigan State University. The author, Matthew Mullen, a freshman, was arrested within two hours and pleaded guilty to making a false report or terrorist threat. He was spared jail time but sentenced to two years’ probation and ordered to pay $800 to cover costs connected to the investigation.

Image A Yik Yak post that prompts a cautionary message.

In the absence of a specific, actionable threat, though, Yik Yak zealously protects the identities of its users. The responsibility lies with the app’s various communities to police themselves by “upvoting” or “downvoting” posts. If a yak receives a score of negative 5, it is removed. “Really, what it comes down to is that we try to empower the communities as much as we can,” Mr. Droll said.