When we first looked atNextdoor five weeks after it launched late last year, the San Francisco-based startup had already helped people create 550 private social networks for their neighborhoods across the country, 100 here in the Bay Area.

Since then it’s grown to encompass 4,000 neighborhoods in 48 states and is adding at least 20 more networks every day.

In order to sign up for this free service, which enhances safety and builds community among the people around you, you need to verify your address and recruit neighbors to join – a minimum of ten people nearby is required.

Each group then gains access to a password-protected website, where they can discuss common concerns, recommend service-providers, list items for sale, find babysitters, and talk about all the kinds of things neighbors used to do face-to-face, back before we all became tethered to digital devices and virtual networks.

Over the course of building up these neighborhood networks, which range in size from around 75 people to up to 7,000 (in Potrero Hill), but often average around 500 households each, Nextdoor has attracted the attention of city officials in many areas.

Nextdoor CEO Nirav Tolia says this usually starts when a city official who happens to live in one of the neighborhoods with a network joins and recognizes its potential to promote civic engagement.

“The city employee tells his colleagues and pretty soon the city comes to us saying ‘we need a better and more efficient way of reaching people and share in bringing back that sense of community to the neighborhoods’.” 

The city can sign up for Nextdoor’s “city program,” and gain the ability to send messages to the various neighborhood groups (though not to read the messages exchanged between neighbors – those remain private.)

The city program got a major boost this week when San Jose, the nation’s tenth largest city, officially endorsed the service after 144 Nextdoor networks – representing more than 40 percent of the city’s neighborhoods – had already joined up.

“We think it will grow to over 350 neighborhoods there in the near future,” says Tolia. “And other cities will follow. The bottom line is cities are having their budgets cut. The Police and Fire Departments can't hire anyone, so we all need to innovate.

“All over the U.S., with the economic challenges we face, how can we foster more civic engagement without spending more money?”

Nextdoor, as a free service, offers just such an opportunity.

“Governments can get creative without spending taxpayer dollars. They can engage in dialogues with residents.”

(One such vigorous dialogue on Nextdoor has been occurring lately in Menlo Park over whether to phase out plastic bags from grocery stores.)

Nextdoor says that 22 percent of the 200,000 messages exchanged a day over Nextdoor networks aleady are focused on these sorts of civic issues.

As for the 4,000 neighborhood networks it has today, the company says that is only the tip of the iceberg when it comes to the future potential for growth.

“We believe there are some 200,000 neighborhoods in the U.S.,” says Tolia. “We'll also explore international markets soon.”

Nextdoor certainly looks like an idea whose time has come. Studies from the Pew Research Center have found that over half of all Americans don’t know any -- or only a few -- of their neighbors by name.

“We've somehow lost touch with our physical surroundings maybe because our virtual surroundings are so rich,” says Tolia.

“So we're not trying to create a new kind of virtual community like Facebook or LinkedIn, but help you get back in touch with the real community where you already live.”

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