President Barack Obama warned American teenagers on Tuesday of the dangers of putting too much personal information on Internet social networking sites, saying it could come back to haunt them in later life.

The presidential words of advice follow recent studies that suggest U.S. employers are increasingly turning to sites such Facebook and News Corp's MySpace to conduct background checks on job applicants.

Taking part in a question-and-answer session with a group of 14- and 15-year-old school students, Obama was asked by one pupil for some advice on becoming U.S. president.

Well, let me give you some very practical tips. First of all, I want everybody here to be careful about what you post on Facebook, because in the YouTube age, whatever you do, it will be pulled up again later somewhere in your life, Obama said.

And when you're young, you make mistakes and you do some stupid stuff. And I've been hearing a lot about young people who -- you know, they're posting stuff on Facebook, and then suddenly they go apply for a job and somebody has done a search.

Obama referred several times to mistakes he had made when he was at school but offered no specifics. He has previously admitted to drug use when he was younger.

A survey in June by found that 45 percent of employers used social network sites to research job candidates and that Facebook, which says it has 250 million users worldwide, was their site of choice.

Some 35 percent of the employers surveyed said they had found content on the sites that had influenced them to reject a candidate. Examples included inappropriate photographs, information about the applicants' drinking or drug use, or bad mouthing of previous employers, co-workers or clients.

The Obama White House frequently uses Facebook, Twitter and other social networking sites to bypass the media and communicate directly to Americans.

(Editing by Phil Stewart)