SAN FRANCISCO — Facebook is trying to coax “news deserts” into bloom with the second major expansion of a tool that exposes people to more local news and information. But the social network confesses that it still has a lot to learn.

The social media giant said Thursday it is expanding its “Today In” service to 6,000 cities and towns across the US, up from 400 in its previous iteration. Launched in early 2018, the service lets Facebook users opt into local news and information from local organizations. Such news can include missing-person alerts, local election results, road closures and crime reports.

The tool lives within the Facebook app; turning it on adds local updates to a user’s regular news feed. In areas with scant local news, Facebook will add relevant articles from surrounding areas.

The service won’t automatically turn on for people even in the areas it serves, which could limit its reach. So far, Facebook says, 1.6 million people have activated Today In. They receive news from some 1,200 publishers every week.

The service aggregates posts from the official Facebook pages for news organizations, government agencies and community groups like dog shelters. It uses software filters to weed out objectionable content.

Facebook employs no human editors for Today In, so tweaking its algorithm to find such good local stories has been a complicated process. Does a road closure matter if it’s 100 miles away? How about a murder?

Some 1,800 newspapers have closed in the United States over the last 15 years, according to research out of the University of North Carolina. Newsroom employment has declined by 45% as the industry struggles with a broken business model partly caused by the success of companies on the internet, including Facebook.

“There is no silver bullet,” said Campbell Brown, head of global news partnerships at Facebook, in an interview. “We really want to help publishers address challenges in local markets.”

Brown, a former news anchor and host at NBC and CNN, said local reporting remains the “most important” form of journalism today. She said Facebook has a “responsibility” to support journalism, while also noting that the media industry has been in decline “for a very long time.”

Local news is just one part of the Today In feature, which also includes posts from local groups along with events and community announcements from schools and governments. A news section within the section shows stories from local newspapers, blogs and TV stations. Facebook isn’t paying licensing fees or sharing ad revenue with these outlets, but says the tool is driving new readers to local news outlets.

Already, Facebook says it’s learned from publishers’ input about what doesn’t work. For instance, it now only allows posts from publishers registered with its “News page index,” which means they meet guidelines such as a focus on current events and information, citing sources and including dates and don’t have a record of publishing false news and misinformation. This means that obituaries from funeral homes, or real estate posts — both of which previously showed up under “news” — are no longer eligible.

The company says publishers featured in Today In see a significant increase “referral traffic” to their websites from Facebook, more so than when people see the same stories in their regular news feed, based on data from its test partners.

″(With the) news feed, people scroll through passively,” said Jimmy O’Keefe, a product marketing manager at Facebook. “We see that people engage with articles more than they would in news feed.”

Outside researchers studying local news data provided by Facebook found that about half of the news stories in the Today In feature met what they called a “critical information need” in the communities it served. This could be helpful for news publishers in determining coverage priorities and for Facebook as it tweaks how it presents news to its users.

Facebook has also learned that local news doesn’t work like national news. Political stories, for instance, don’t generate a lot of local interest.

When researchers looked at the types of news stories Facebook showed and how users interacted with them, finding that Facebook users interacted the most with stories serving a critical need — such as information on emergencies, transportation and health. While there were more “non-critical” stories available, on sports, for instance, people didn’t interact with those to the same degree. The researchers —Matthew Weber at the University of Minnesota and Peter Andriga and Philip Napoli at Duke University —received no funding from Facebook.

The expansion to 6,000 cities still doesn’t include large metro areas such as New York City, Los Angeles or San Francisco, where the abundance of news and population density makes it more difficult to provide relevant local information. A big local story in Brooklyn, for instance, might be irrelevant on Staten Island just a few miles away.