It was early in the morning when the flooding hit The Knolls, a neighborhood of about 500 homes in Columbus, Ohio. The sewer overflowed, dumping a foot and half of water into Chuck Totten’s basement, where his wife Deb kept around $25,000 worth of fabric and sewing supplies. A retired financial analyst in poor health, Totten was distraught and unable to climb up and down the stairs carrying all the heavy loads of soaking material himself. So he put out a call for help on Nextdoor, a private social network aimed at connecting neighbors.

"It was like living in an Amish community."

"It was like living in an Amish community, and somebody had rung a bell, ‘cause people just came out of the woodwork to help," remembers Totten. While similar cries for help had been posted to services like Twitter and Facebook, it was the Nextdoor message that brought real humans to his door. "Most social media is people you know, sure, but it's not the people around you, living in your town. Being able to make that connection is a really powerful thing."

Founded in 2010 and based in San Francisco, Nextdoor is a odd outlier among today’s social networks. Signing up is an onerous process, requiring substantial proof of both your identification and address. People post messages, but they are seen only by others in the immediate area, and there is no share or retweet button to proliferate messages across the network. It feels more like a modern update on a message board or web forum than a social network. But it has struck a chord across the country. When The Verge first reported on Nextdoor back in July of 2012, it was in 3,500 neighborhoods. Today, the company is announcing that its reached 40,000 neighborhoods, or roughly one in four American communities, with 10 or more active users.

The company’s success parallels a troubling trend. The rise of social networks means many people have hundreds or even thousands of digital connections to old friends, co-workers, and acquaintances. But increasingly that wealth of online companionship corresponds with a loss of close relationships to the real-life human beings in our neighborhoods. A third of Canadians and half of Americans admitted in studies that they don’t know the names of any neighbors. In the UK, one in three people couldn’t pick their neighbors out of a police lineup.

Two new books, Marc Dunkelman’s The Vanishing Neighbor and Susan Pinker’s The Village Effect, chronicle these trends and their impact on our bodies and our body politic. Dunkelman sees it at the root of America’s increasingly polarized politics and disaffected voters. For Pinker, a sociologist, the effects run deeper. She notes that the more overlapping relationships among friends, family, and neighbors, the better a person’s prognoses with the most life-threatening diseases and the lower the instances of debilitating illness like dementia. Getting to know your neighbors is statistically shown to produce a longer, healthier life.

Knowing your neighbors is good for your health

Ironically, an online service seems to be a popular way to rekindle the human connections that many have lost, and still hunger for. "I started out using Nextdoor to ask for things like restaurant recommendations, just kind of a local search engine," says Matthew Tortorella, a police officer in San Diego. "But after a while people would recognize me on the street from my Nextdoor profile, and strike up a conversation or just say hi." Asked why he wasn’t meeting his neighbors before, Tortorella said it felt more natural this way. "It’s weird, I guess, but, having these interactions online was really the thing that led to finally meeting people face to face."

Tortorella is also one of many police officers who use Nextdoor as part of the everyday work in law enforcement. "It has been this amazing extension of the community watch and opened up channels of communication between officers and citizens," he explained. "A lot of people don’t want to call us unless there is something serious, but they are comfortable asking questions of their local officer over Nextdoor on a weekly, sometimes daily, basis."

"It was the kind of small thing that might have gone unremarked."

Recently, a Nextdoor user in from San Diego PD’s Northwest division sent a message to the local officer about an unfamiliar truck parked facing the wrong direction on their street. Police followed up on the tip and found the car was stolen. Evidence inside led them back to a suspect who had a committed a rash of recent burglaries. "It was the kind of small thing that might have gone unremarked if a phone call was required, or if the citizen who made the call wasn’t as familiar with their local officer through Nextdoor," says Tortorella.

One of the big differences between Nextdoor and other services like Yahoo or Facebook groups is ability to see each member’s address and push messages and alerts based on geography. Nextdoor users can see messages and alerts on the website, but also can sign up to receive email and push notifications. "We had some pretty big wildfires here recently and we used Nextdoor to send out evacuation alerts," says Tortorella. "Because it allows us to target areas of the map, only people in that zone would get the warning."

Right now, Nextdoor doesn’t have any revenue. The company has raised a little over $100 million in venture capital, and both its executives and investors seem content to continue focusing on user growth before trying to build a business. "We have plenty of money in the bank and want to continue optimizing the service to meet the demands of our users," says CEO Nirav Tolia. "But naturally, as our communities have grown, more and more the content people are posting is transactional in nature." Down the line, says Tolia, Nextdoor could make money by serving as a marketplace for that used couch, or showing ads from a local plumber or babysitter next to a question from a user about where to find those services.

"An unpleasant sobering to the reality that things are not as pleasant as they previously thought."

Because Nextdoor is private, the citizens and officers interviewed for this piece were volunteers who responded to a a broad interview request. But not everyone shared only positive experiences. Many users mentioned that it had added a touch of paranoia to their lives. "Some folks who were previously only communicating with a small handful of fellow residents are somewhat dismayed when they are made aware of the crime and other unpleasant occurrences," says Darell O’Quinn, who leads the Crestwood neighborhood Nextdoor in Birmingham, Alabama. "For some people this amounts to bursting the bubble of their perception and an unpleasant sobering to the reality that things are not as pleasant as they previously thought."

Still, most Nextdoor users say it’s healthy to air their neighborhood’s dirty laundry, and prefer a service that keeps the discussion limited to people who can prove they are living in the immediate vicinity. "Other social media is open to the world. As odd as it may seem, there are people who troll neighborhood groups," says O’Quinn. Nextdoor is where people can openly talk about local problems without worrying they will harm property values. "Because of the sensitivity to how the neighborhood is broadly perceived, some of that information can be stifled in an environment that is open for global inspection. We use Facebook, Twitter, and other social media, but Nextdoor is where most of the real conversation happens."