Facebook's mystery announcement Tuesday turned out to be what it calls "Graph Search," a beta social search engine to find things on Facebook like "Friends of friends who are single men in San Francisco?" or "Friends of current employees," a good place to start for recruiting.

It's supposed be a non-web search service geared to the people, photos, places and interests listed on Facebook that doesn't compete with Google. But it does and if Facebook successfully develops the widgetry, well, it could be extended now couldn't it and threaten Google's ad business.

Even at this point it promises to replace some Internet searches with what is essentially custom content. No sense searching for a restaurant or a club if you can see where your friends have gone.

Shares of Google and Yelp, the online directory service, were both depressed on the news.

Graph Search is meant to navigate the Internet through the data Facebook owns. Searches can be refined so they're unique to the searcher and the widgetry is supposed to be privacy-aware. You can only search for content that's been shared with you.

Graph Search is different from web search, which delivers answers with links. Graph Search just delivers the answers.

Facebook CEO Mark Zuckerberg said, "Graph search is a really big product. It's going to take years and years to index the whole map of the graph and everything we have out there."

"We'll start rolling it out very slowly. We're looking forward to getting into more people hands over the coming weeks and months."

The announcement was Facebook's first big event since its awful $100 billion IPO in May. Its Q4 financial results, expected to show improvement in its mobile ad billings, are due January 30.

There's more to this search thing.

Facebook is going to use Bing - not Google - to deliver search results from outside its on-site Graph Search. Bing results, like weather, will be tagged web results, indicating that they are coming from off-site.

In 2007, Microsoft tucked $240 million in the start-up giving it a $15 billion valuation.

Bing was integrated into Facebook last year. It's now apparently part of Facebook's "unified search."

Oh, by the way, in case you don't know Facebook calls the widgetry Graph Search because it's taken to calling its growing content, data and membership the "social graph."

Ovum principal analyst Eden Zoller reflects that "Before the arrival of Facebook's Graph Search, the search function on Facebook was basic and as such, a wasted opportunity given Facebook's imperative to strengthen advertising revenues. Facebook Graph Search will no doubt leverage member data to provide advertisers with more targeted, personalized advertising opportunities going forward. But Facebook needs tread very carefully here and be mindful of user privacy. It claims to have built Graph Search with privacy in mind, but Facebook has a mixed track record on this front and is in the habit of pushing privacy to the limits of what is acceptable."

See www.bing.com/community/site_blogs/b/search/archive/2013/01/15/sof.aspx.