The feature allows users to make "natural" searches of content shared by their friends. Search terms could include phrases such as "friends who like Star Wars and Harry Potter".
Founder and chief executive Mark Zuckerberg insisted it was not a web search, and therefore not a direct challenge to Google. However, it was integrating Microsoft's Bing search engine for situations when graph search itself could not find answers.
Mr Zuckerberg said he "did not expect" people to start flocking to Facebook to do web search. "That isn't the intent," he said. "But in the event you can't find what you're looking for, it's really nice to have this."
Earlier speculation had suggested that the world's biggest social network was about to make a long-anticipated foray into Google's search territory.
"We're not indexing the web," explained Mr Zuckerberg at an event at Facebook's headquarters in California. "We're indexing our map of the graph - the graph is really big and its constantly changing."
In Facebook's terms, the social graph is the name given to the collective pool of information shared between friends that are connected via the site.
Source: BBC News
