Facebook CEO Mark Zuckerberg introduced a new function today called “Graph Search.”

Until now, Facebook users have not been able to do detailed searches of the social network’s piles of data, and Google and others can’t access much of what’s on Facebook to do it for them.

“The thing about Facebook is it has all this data,” Marketplace’s Queena Kim says. “That’s totally a blind spot for Google. And as Google gets more into things like restaurant reviews, this is all the personal information they can’t access.”

Right now Facebook’s search is limited to a few categories: People, Photos, Places and Interests.

Here’s how it works:

“Let’s say I meet somebody interesting at your party, Kai,” Kim says. “But I only get their first name George and that he went to college at Berkeley.” Depending on privacy settings: “Now I can enter ‘George,’ ‘Berkeley,’ ‘Kai,’ and his name should pop up.”

The Graph Search is in Beta. And Zuckerberg stressed again and again that it’s being released to a limited number of people: some hundreds or thousands.

But we got a glimpse of who should be worried in the examples they gave. You can use search right now to see what restaurants your friends like — possibly a threat to Yelp.

Of course, users will also be concerned about their privacy. One solution is to untag photos or ask Facebook to remove them. But if users don’t take that step, pictures of them may be accessible to more people than ever.

“All those embarrassing pictures that your mom or sister or brother is posting, they’re going to pop up,” Kim says.