Sacramento Police Chief Sam Somers Jr. says a private social media site is making his department more effective.

A year ago, the Sacramento Police Department launched a partnership with Nextdoor, a young San Francisco company that connects residents of individual neighborhoods in cities where it operates.

“We know there’s a lot of power in social media,” Somers said during a news conference Thursday to announce the results of the partnership.

There are now 18,000 members of Nextdoor in 116 Sacramento neighborhoods, said company spokeswoman Kelsey Grady. More than 85 percent of Sacramento neighborhoods are on the free site, which requires members to verify their addresses and use their real names.

The Police Department has posted more than 500 crime and safety alerts and initiated conversations. Neighbors can respond to the police posts and communicate with officers through a thread of replies.

Nextdoor’s platform for instant communication through alerts has proved to be an useful tool to build stronger and safer communities, City Councilman Jay Schenirer said.

“I think that the safety of a community is in the hands of the community,” he said.

Angela Wood of the Pocket moderates her neighborhood’s site. She said she’s on Nextdoor constantly, posting crime updates. Wood not only serves as a watchdog for Pocket, but also shares crime and safety information for her surrounding neighborhoods.

“We don’t have a lot of crime in our area, but we don’t want it to get to the point where the little things add up,” she said. “When little things happen, we’re on it.”

The partnership has helped the Sacramento police solve criminal cases, said Capt. Bill Champion Jr. Watchdog neighbors noticed drug dealing in the Alkali Flat neighborhood north of downtown in March.

The Nextdoor users posted a photo of the suspected drug dealers’ vehicle, provided specific descriptions of activities occurring and the time and date the drug deals happened, Champion said. Officers went out the next morning, located the van and arrested two people on suspicion of possessing a controlled substance for sale.

The initiative taken by the neighborhood citizens streamlined the tip process, Champion said.

“Years ago, we maybe needed a tip to come in and it could be weeks before it got to us,” he said. “The fact that citizens are more involved gets us more information.”

Every private Nextdoor site is launched by someone in the community, Grady said. Neighbors use the web and mobile site to chat about community, events, classifieds, recommendations and crime and safety.

Nextdoor has been able to remain free for users because it raised $100 million in venture capital funding, Grady said. The startup is still figuring out how it will eventually make money on its social media platform while keeping it free.

Nextdoor will likely wind up using advertising to connect local businesses to neighbors, like a “new-age Yellow Pages,” Grady said.