Called "graph search", the new service unveiled by CEO Mark Zuckerberg lets users quickly sift through 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 favourite TV shows of all their friends who happen to be doctors.
Although Zuckerberg stressed that "graph search" is different from an all-purpose search engine, 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.
"This could be another reason not to use Google and another reason to stay on Facebook for longer periods," said technology expert Brian Blau.
"I don't think Google is going to lose its search business, but it could have an impact on Google by changing the nature of search in the future."
Facebook's foray into search marks one of its boldest steps since its initial public offering of stock flopped eight months ago amid concerns about the company's ability to produce the same kind of robust earnings growth that Google delivered after it went public in 2004.
If the new search tool works the way Facebook envisions, users should be able to find information they want to see on their own instead of relying on the social network's formulas to pick which posts and pictures to display in their fees, analysts said.
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.
And Facebook's users will be able to enter search terms the same way that they talk, relying on natural language instead of a few stilted keywords to telegraph their meaning.
Only a fraction of Facebook's more than 1bn users will have immediate access to the new search tool because the company plans to gradually roll it out during the next year to allow time for more fine tuning.
Not all the interests that people share on Facebook will be immediately indexed in the search engine either, although the plan is to eventually unlock all the information in the network while honouring each user's privacy settings.
That means users can only see content that's available to them through other's privacy settings, Zuckerberg pledged.
"Every piece of content has its own audience," he said.
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.
Facebook's decision to make its foray into search slowly reflects the formidable challenge that it's trying to tackle.
The social graph is big and changing, Zuckerberg said.