To join, you have to prove you live where you say you do — providing your home telephone number for a verification call, for instance. Or a vetted neighbor can vouch for you, which is how Nextdoor said most people end up joining.
Of the approximately 2,000 Nextdoor neighborhood sites, 20 are in Maryland. Seven more are in the pilot stage locally, waiting for enough sign-ups.
The company says it eventually will look for ways to generate revenue — probably by connecting neighbors with local businesses — but is focusing for now on helping users solve daily problems.
"Probably hundreds of baby sitters are found every day, lost pets are found, crimes are reported," said Tolia, who co-founded online review site Epinions before launching Nextdoor. "In Woodside, Calif., there was a woman whose son was diagnosed with meningitis, and she got the word out through Nextdoor."
Rohit Bhargava, a marketing expert whose book "Likeonomics" is due out in May, said there does seem to be a neighborhood gap unfilled by Facebook and other social-network behemoths. He thinks the trick for a would-be contender is to reach neighborhood "influencers" — the people who can mean the difference between success and failure for an enterprise that boils down to word of mouth.
Then there's the challenge of persuading people used to not knowing their neighbors that they ought to.
"If you asked people directly, 'Would you like to know and have more connections with [your] immediate neighbors,' there are probably a lot of people who would say, 'You know, I don't really care about that,'" said Bhargava, who teaches marketing at Georgetown University. "But if they actually experienced having better connections with their neighbors … I think most people would get value out of that."