A Facebook for crime fighters E-mail Tweet Facebook Google Plus Linkedin Share icons by Miguel Helft @FortuneMagazine July 1, 2014, 11:52 AM EDT Most of us don’t want the cops to pop up in our social-networking news feed. But to Mary Boergers, there’s something comforting about it. A retired legislator and community activist who lives in Oakland, who has little interest in sites such as Facebook or LinkedIn, Boergers enjoys getting updates from local police officers via Nextdoor, a two-and-a-half-year-old site that is carving up its own niche in the saturated social-networking universe. “The police are sharing information, and that’s very positive,” Boergers says. If Facebook is for friends and family, Twitter for celebrities and interests, and LinkedIn for colleagues and career, Nextdoor is for neighbors. Of course, a neighborly thing to do is to look out for one another, and that’s where the cops come in. “I view Nextdoor as neighborhood watch for the 21st century,” says Lt. Chris Bolton of the Oakland Police Department, who helped pilot his department’s partnership with Nextdoor, announced in April. Police weren’t always part of Nextdoor. The service—a collection of tens of thousands of localized mini-networks—began as a place for neighbors to recommend gardeners and babysitters, advertise garage sales, and ask for help finding a lost pet. But as it grew quietly to nearly 37,000 neighborhoods, up from 12,000 a year ago, some of its most engaged members said they wanted to hear from their police officers. Nextdoor had to tread carefully, because one of its marquee features is limiting participation to verified residents of a neighborhood. Eventually the site agreed to let police departments pipe in to alert residents about a road closure or a surge in burglaries, ask for tips to solve a crime, or warn residents about a suspected criminal. Residents can respond, but officers who don’t live in the neighborhood cannot see other posts on the site. For better or worse, public safety has become one of Nextdoor’s killer apps. After every new “partnership” allowing a police agency to join, activity on Nextdoor neighborhoods surged—230% in Dallas, 200% in San Diego. That led co-founder and marketing chief Sarah Leary to argue for a complete revamp of Nextdoor to allow police departments and other public agencies, like cities or transit systems, to participate more easily and effectively. The Nextdoor City Platform, which launched in June, makes it much easier for officials to post to specific neighborhoods and send real-time alerts from their smart-phones. And it should help Nextdoor, which has formed more than 170 partnerships with police departments and agencies, add new cities at a much faster clip, potentially leading to a new phase of growth for the site. The move, one of the largest engineering efforts at the company since its founding, is a gamble by Nextdoor’s investors— top venture firms like Benchmark, Greylock, and Kleiner Perkins Caufield & Byers. Crime fighting is not monetizable (and Nextdoor has yet to bring in any revenue), but investors believe increased engagement on public safety will pay off in other ways, for instance, helping to make the site even more appealing to local advertisers. “Because of the utilitarian nature of Nextdoor monetization is going to be incredible and much higher than it has been in other social networks,” says Benchmark’s Bill Gurley, whose firm also invested in Twitter before it started monetizing its service. Nextdoor’s image as a crime-fighting tool suffered a hiccup last month, after the company’s own CEO, Nirav Tolia, was charged with a felony in a hit-and-run for leaving the scene of accident he helped to cause. The case was resolved after Tolia pled “no contest” to lesser misdemeanor charges. As the case unfolded, several police departments contacted by Fortune said they saw Nextdoor as a useful tool and planned to continue using it. And new cities, such as Pittsburgh, have begun working directly with NextDoor to improve their outreach. Whether Nextdoor can help reduce crime is another matter. At this point, the evidence is anecdotal. But tech-savvy cops say it’s helping in myriad ways. “It has other effects, like reducing the fear of crime and increasing the sense of community,” Lt. Bolton says. Score one for community policing in the Digital Age.