After building neighborhood social networks in more than 3,000 communities across the U.S., Nirav Tolia has learned just how many different things neighbors can accomplish. Using Nextdoor, the site built by Tolia and his team, neighbors get burglars arrested, investigate possible water poisoning, and stop the installation of parking meters. They lend one another ladders and grills, recommend babysitters, and upload videos of locals.

But the one thing they're not looking to do is make friends.

"You're not friends with your neighbors," Tolia says. "You don't want to be friends with your neighbors... The communication is a lot more high fidelity if the context is clean.

"With your neighbors, everyone can get fired up about the pothole, and that's something that your Twitter followers and your friends and your business colleagues just don't care about... On Facebook, I'm going to be posting about my birthday."

Tolia might be on to something. A Pew study released last year found that neighbors comprise just 2 percent of a typical American's Facebook friends, eclipsed by high school and college buddies (31 percent), family (20 percent) and coworkers (10 percent).

At Topix, a favorite online gathering place for small-town Americans, the community discussion boards aren't tender or cuddly."Mostly they'll fill it up with stuff like interpersonal gossip," says Topix CEO Chris Tolles. "Once you get beyond like two doors down, that person is outside of your general social interaction... People kind of know each other, but not really."

There's a prominent line of thinking that says that the internet has weakened our emotional ties and friendships by encouraging us to communicate in isolation. But physical distance is actually better for deep emotional ties, if the experiences of Nextdoor and Topix are any indication. It turns out people, at least in America, tend to be not particularly friendly with the people closest to them and their families, but connect famously to people on the other side of the country. Why is that?

It might be that we're not friends with our neighbors because we're moving and traveling more than we used to, suggests urban studies professor and author Richard Florida. Knowledge workers and other members of what Florida famously dubbed the growing "Creative Class" tend to create neighborhoods with "little in the way of tight bonding and social capital," Florida, says, citing research by his former student Brian Knudsen as well as by the sociologist Robert Cushing.

In other words, people are creating practical ties around specific goals, or engaging in what Florida refers to as "involvement in protests." That is, things like nixing a city parking meter plan, as Nextdoor members have done, or fighting a new waste treatment plant, as Topix members have done.

This sort of targeted action happens to be an area where Facebook is weak. Observers like social software guru Clay Shirky believe goal-oriented online groups will be behind the next reinvention of social networking, particularly after social media played such a prominent role in the Occupy movement and in the Arab Spring.

Both Tolia and Tolles believe they can help turn neighbors into something much more powerful than groups of friends. Tolia added a feature enabling neighbors to send urgent text alerts to one another when they see crime happening. "We literally believe that we can bring down crime rates," he says. Nextdoor recently announced it was adding 20 new communities a day to its current network of 3,300 U.S.-based neighborhoods, and Tolia thinks it can grow to 200,000 in the U.S. alone.

Meanwhile Tolles has launched a national political site, to be fed by grassroots reporting informed by the sometimes vicious local gossips he's attracted to his forums. "There are people who exposed all sorts of weird local corruption, there are people who have outed murderers, there's lots of cool stuff in there," he says.

You might not want to be friends with your neighbors, but you do want to keep in touch. If you do, who knows? Maybe that network will become as important to you as Facebook. And the company that gets those fence-line relationships right just as valuable.