Nextdoor raises $21.6 million led by Greylock to expand and focus on neighborhood safety

Nextdoor, the private social network created for individual neighbors to connect around their location, plans to announce Tuesday a new funding round of $21.6 million led by Greylock Partners. The company said it has seen rapid growth, doubling the number of neighborhoods it’s entered in the past six months, and is also launching a redesign Tuesday that places emphasis on flagging crime and safety, an area where the social network thinks it can excel.

Nextdoor demo newsfeedThe new funding is led by Greylock Partners and includes existing investors Benchmark and Shasta Ventures, as well as new investors Bezos Expeditions and Google Ventures. Greylock’s David Sze, who has invested in Facebook (s FB), Digg, and LinkedIn (s LNKD), is joining Nextdoor’s board. The company just raised $18.6 million in July 2012, which at the time put the startups valuation at over $100 million. The company did not disclose a valuation based on this funding round, but a spokeswoman said:

“It’s a healthy step up from the last round and reflects the optimism of our experienced investors.”

CEO Nirav Tolia said the company is now launching more than 30 neighborhoods a day, which is not an easy process when a minimum threshold of users need to verify their address to join, both ensuring security around the site and making sure no one experiences the “empty party” phenomenon that can kill a social network’s success:

“This is not a West Coast thing or affluent or tech savvy or young person thing,” he said. “Everyone wants to connect to their neighborhoods.”

In June the company partnered with National Night Out to promote neighborhood safety, and it has further plans for expansion. The new version of Nextdoor will include divided sections (including one for crime and safety), the ability for police officers in large metro areas to connect with residents and give safety tips, and the ability for users to send urgent alerts to fellow neighbors in case of emergency.

The new version of Nextdoor will also allow users to share information like a lost cat with nearby neighborhoods, rather than limiting them to their own location, and will divide up the types of posts into sections, like crime and safety and classifieds. The company launched in October 2011, and aims to capture a new market for social media outside of LinkedIn and Facebook and Twitter. The question is whether users will continue to flock to Nextdoor as the company’s competitors keep growing and moving into new territory as well.