SAN FRANCISCO -- Facebook's greatest triumph has been to persuade a seventh of the world's population to share their personal lives online.
Now the social network is taking on its archrival, Google, with a search tool to mine that personal information, just as people are growing more cautious about sharing on the Internet and even occasionally removing what they have already put up.
Whether Facebook's more than one billion users will continue to divulge even more private details will determine whether so-called social search is the next step in how we navigate the online world. It will also determine whether Facebook has found a business model that will make it a lot of money.
"There's a big potential upside for both Facebook and users, but getting people to change their behaviors in relation to what they share will not be easy," said Andrew T. Stephen, who teaches marketing at the University of Pittsburgh and studies consumer behavior on online social networks.
This week, Facebook unveiled its search tool, which it calls graph search, a reference to the network of friends its users have created. The company's algorithms will filter search results for each person, ranking the friends and brands that it thinks a user would trust the most. At first, it will mine users' interests, photos, check-ins and "likes," but later it will search through other information, including status updates.
"While the usefulness of graph search increases as people share more about their favorite restaurants, music and other interests, the product doesn't hinge on this," a Facebook spokesman, Jonathan Thaw, said.
Nevertheless, the company engineers who created the tool -- former Google employees -- say that the project will not reach its full potential if Facebook data is "sparse," as they call it. But the company is confident people will share more data, be it the movies they watch, the dentists they trust or the meals that make their mouths water.
The things people declare on Facebook will be useful, when someone searches for those interests, Tom Stocky, one of the creators of Facebook search, said in an interview this week. Conversely, by liking more things, he said, people will become more useful in the eyes of their friends.
"You might be inclined to 'like' what you like so when your friends search, they'll find it," he said. "I probably would never have liked my dentist on Facebook before, but now I do because it's a way of letting my friends know."
Mr. Stocky offered these examples of how more information may be desirable: A single man may want to be discovered when a friend of a friend is searching for eligible bachelors in San Francisco or a restaurant that stays open late may want to be found by a night owl.
"People have shared all this great stuff on Facebook," Mr. Stocky said. "It's latent value. We wanted a way to unlock that."
Independent studies suggest that Facebook users are becoming more careful about how much they reveal online, especially since educators and employers typically scour Facebook profiles.
A Northwestern University survey of 500 young adults in the summer of 2012 found that the majority avoided posting status updates because they were concerned about who would see them. The study also found that many had deleted or blocked contacts from seeing their profiles and nearly two-thirds had untagged themselves from a photo, post or check-in.
"These behavioral patterns seem to suggest that many young adults are less keen on sharing at least certain details about their lives rather than more," said Eszter Hargittai, an associate professor of communication studies at Northwestern, who led the yet unpublished study among men and women aged 21 and 22.
Also last year, the Pew Internet Center found that social network users, including those on Facebook, were more aggressively pruning their profiles -- untagging photos, removing friends and deleting comments.
Graph search is something of a coming-of-age moment for social search. Companies from Google to Yelp to TripAdvisor to small start-ups like Hunch have all tried to make search more social, by providing personal answers from people you know and not just links to Web sites, in an effort to bring word-of-mouth recommendations online. Bing, which has a partnership with Facebook, announced this week that it would add more social recommendations to standard Web links in search queries.
But no company has tried social search on Facebook's scale.
"This is a watershed moment," said Oren Etzioni, a computer science professor at the University of Washington and a co-founder of the price comparison site Decide.com.
"There have been other attempts at social search," he continued, "but it's the scale at which Facebook operates, especially once they fully index everything we've said or say or like."
Facebook's social search is also a step forward in a new type of Web search, one in which Google has made great strides. Engineers call it structured or semantic search, which means search engines that understand how people, places and things relate to one another, and not just key words.
Graph search holds great value for advertisers seeking to target more precise audiences -- like mothers in their 30s who listen to hip-hop and run marathons -- and advertising remains Facebook's principal source of profit. Additionally, the more data people share and search for, the longer they are glued to the site.
But the company is aware of concerns about privacy. When announcing the tool, it took pains to point out that it would respect users' privacy. If people do not want an embarrassing photograph to be ferreted out by a potential employer, for instance, they can make it visible only to those who have been winnowed down as "close friends."
Users have been encouraged to check their privacy settings in order to fine-tune whom they wish to share with. At the same time, Facebook eliminated a longstanding option that users enjoyed: if someone is searching for them, they will no longer be able to remain obscure.
Still, some Facebook users may be skeptical. Jana Uyeda, 35, a photographer and social media consultant in Seattle, said, "I love my friends, but sometimes their taste in restaurants is terrible."
Like the subjects of the Northwestern study, Ms. Uyeda, said she was not so sure she wanted to reveal more. "I'm slowly trying to close down the doors on Facebook, instead of opening myself up," she said.
Ms. Uyeda added, "There would have to be a lot of other incentives, and I don't even know what that would be, in order for me to add more information about myself and be more open."interact
This article originally appeared in The New York Times.