Called "graph search," the new service lets users search their social connections for information about people, interests, photos and places. It'll help users who, for instance, want to scroll through all the photos their friends have taken in Paris or search for the favorite TV shows of all their friends who happen to be doctors.
Until now, Facebook users were unable to search for friends who live in a certain town or like a particular movie. With the new feature, people can search for friends who, say, live in Boston who also like "Zero Dark Thirty".
Zuckerberg says the search feature is "privacy aware," which means users can only search for content that has been shared with them. Still, the company will have to make it clear to users that the new feature isn't unearthing information about them that wasn't already available.
Facebook is stressing that graph search will be made available to users very slowly, beginning Tuesday. Though the company has focused on refining its mobile product for much of last year, the search feature will only be available on Facebook's website for now, and only in English. It will likely take more than a year for search to be available to all of Facebook's more than 1 billion users as the company's engineers and designers tweak the service based on how people use it.
Though Zuckerberg stressed that "graph search" is different from traditional Web search, the expanded feature escalates an already fierce duel between Google and Facebook as they grapple for the attention of Web surfers and revenue from online advertisers.
Although Facebook isn't trying to fetch information across the Web like Google does, it's clearly trying to divert traffic and ad spending from its rival. Facebook is hoping to do this by making it easier for its users to quickly find many of the things that are most important to them: movie, music and restaurant recommendations from friends and family; photo galleries of people they care about; and new connections to old friends and other people with common interests.
It's the kind of personal data that has been difficult for Google to collect, partly because Facebook has walled off its social network from its rival's search engine. Instead, Facebook has partnered with Microsoft Corp. to use its Bing search engine to power traditional Web searches done through its site. That partnership remains.
Zuckerberg acknowledged that it's unlikely that many people will visit Facebook to do traditional Web search. But that doesn't mean they shouldn't be able to.
"There is a lot of content you can find on graph search but there is a lot you can't," he said. "It's much better to show world-class Web search results...than to show nothing."
Google is trying to overcome its social network disadvantage with Google Plus, a service that the company launched 19 months ago in attempt to glean more insights into people's relationships and counter the threat posed by Facebook.
Helped by Google's aggressive promotion of the service, Plus boasts more than 135 million people who post information and photos on their profiles. But Google Plus users still aren't sharing as much or hanging out on its service as long as Facebook users do, raising questions about whether Google will ever be able to get a grasp on the Internet's social sphere as firmly as Facebook does.
Facebook now must prove it can master the intricacies of search and picking the right ads to show to the right people at the right time - complicated tasks that Google has honed during the past 14 years to establish itself as the Internet's most powerful company. It currently produces 10 times more annual revenue than Facebook. Though neither company has released its 2012 financial results, analysts are projecting $52 billlion in 2012 revenue for Google versus about $5 billion for Facebook. For now, there is no advertising component to Facebook's search feature.
Zuckerberg hinted last fall that a search feature was in the works in his first post-IPO public interview. But investors - some of whom may have been hoping for a long-rumored and always-denied "Facebook phone" - didn't seem impressed.
Facebook's stock slid 50 cents to $30.45 following the announcement. It's still down nearly 20 percent from its IPO price of $38. The stock has enjoyed a healthy uptick so far this year, however. It's up about 14 percent year-to-date, and trading above $30 for the first time since July.
AP Technology Writer Michael Liedtke contributed to this story from San Francisco.