Facebook now accounts for 1% of all net traffic

The function will initially allow anyone who is not registered with the site to search for a specific person.

More controversially, in a month's time, the feature will also allow people to track down Facebook members via search engines such as Google.

The firm said that the information being revealed is minimal.

Privacy erosion

The public search listing will show the thumbnail picture of a Facebook member from their profile page as well as links allowing people to interact with them.

But, in order to add someone as a friend or send them a message, the person will have to be registered with Facebook.

Users who want to restrict what information is available to the public or opt out of the feature altogether can change their privacy settings. They have a month to do so.

Despite assurances from Facebook, critics have expressed disappointment at the move.

"This move transforms Facebook from being a social network to being a quasi-White Pages of the web," commented technology writer Om Malik in his blog GigaOm.

Mr Malik, and others, are concerned about the data trail that people are routinely leaving behind them on social networking and other sites.

There are concerns that personal content will become aggregated for marketing or other purposes.

Security experts have pointed out the dangers of publicising your date of birth - one of the options in a Facebook profile - because of the way it has been traditionally used as a way of identifying bank customers.

Facebook began life as a way of keeping US college students in touch with each other. Devised by Harvard drop-out Mark Zuckerberg, the site now accounts for 1% of all net traffic and is the sixth most visited site in the US

The social networking site is thought to have about 39 million members. Numbers have jumped since the firm removed the need to have an academic e-mail address in September 2006.