Nextdoor, a Network for Neighborhoods, Attracts Early Backer of Facebook and LinkedIn Facebook is where people promote how cute their kids are, and LinkedIn is where they promote themselves. Nextdoor is where they promote their need to borrow a ladder. Now Nextdoor, a San Francisco-based Web site for connecting neighbors, has something else in common with its far bigger and better known peers in the social networking trade: the same early investor. Greylock Partners, a venture capital firm that made investments years ago in LinkedIn and Facebook, has led a $21.6 million financing round in Nextdoor. David Sze, the Greylock partner who invested in those other companies, will join Nextdoor's board of directors. New investors participating in the funding also include Google Ventures and Bezos Expeditions, the investment firm of Jeff Bezos, the Amazon.com chief executive, along with existing investors Benchmark Capital and Shasta Ventures. In total, the company has raised $40.2 million. Nextdoor first opened for business in late 2011 and is now available in 8,000 neighborhoods in all 50 states. That number is more impressive when you consider that the Nextdoor networks for all of those neighborhoods were started by a person who lived in that neighborhood and then successfully recruited at least nine other neighbors to join. Only people who actually live in a neighborhood are eligible to join the Nextdoor network for their area and everybody has to use their real identities on the site, which Nextdoor says is essential for keeping the quality of conversations on the site high. Nextdoor verifies that you live where you say you do either by checking your credit card record, making an automated phone call to your home number or by sending a postcard to your house with a registration code on it. The company sends out 15,000 such postcards a day, according to Nirav Tolia, the chief executive of Nextdoor. "It's a lot of friction to join," he said. Mr. Tolia declined to say how many people are members of Nextdoor. In an interview at his office in San Francisco, Mr. Tolia showed a slide with a bar chart breaking down the most common uses for Nextdoor. Recommendations (for baby sitters, good mechanics and the like) and posts about a local break-in and other crime and safety issues are among the top two categories. Neighbors are also using it as a hyperlocal version of Craigslist, where they send out requests to borrow shop vacs and other infrequently used items or advertise piles of bricks and other free items they'd like to get rid of. Nextdoor has revamped its Web site to make it easier for people to sort posts in their neighborhood by categories, and the company is also allowing people to post messages to adjacent neighborhood networks on Nextdoor (lost cats don't necessarily recognize neighborhood boundaries). Mr. Sze of Greylock said most of the connections on Facebook are between people who already have an existing relationship, but Nextdoor is connecting people who very often don't know each other, even though they live in close proximity. "The fascinating thing about Nextdoor is there's this latent desire to connect with people around you," he said.