Nextdoor, a San Francisco startup that operates social networks for more than 3,500 neighborhoods across the country, has raised $18.6 million in financing from a large syndicate of investors that includes Benchmark Capital, DAG Ventures, Greylock Partners, Shasta Ventures, Allen & Company and Pinnacle Ventures. Among other things, consumers use Nextdoor to answer questions from their neighbors; promote community events; post weather and traffic bulletins; and report crime and emergency alerts. In addition, neighbors can sell goods through the site in an online marketplace similar to Craigslist, except in the case of Nextdoor you have the knowledge (and comfort) that buyers or sellers live nearby. "Facebook is the best way to connect to friends and family, and LinkedIn is the best way to connect to business contacts — now Nextdoor has created the best way to connect to neighbors," said Greylock's David Sze in a release.