The U.S. Department of Justice, the Ad Council, and the National Center for Missing and Exploited Children have launched a "Think Before You Post" campaign to discourage teenage girls from posting personal information online.

In announcing the initiative last week, the groups said that sites like MySpace and Facebook make it easy for teens to give out personal information, videos, and pictures, which make them more vulnerable to online predators. The main Web page for the campaign includes a game called "ID the Creep."

Sixty-one percent of teens between the ages of 13 and 17 have personal profiles on MySpace, Friendster, Xanga, or other sites, and half posted pictures of themselves online, according to a study by Cox Communications.

One out of five teens reported that they believed it was somewhat or very safe to share personal information on blogs or networking sites. Thirty-seven percent said they were not very, or not at all, concerned about people using personal information they have posted in ways they haven't approved.

The groups behind Think Before You Post said teenage girls particularly are at risk of online sexual exploitation. They cite a University of New Hampshire study that concluded one in seven youth are sexually solicited or approached over the Internet, and 70% of them were girls.

Researchers at the University of New Hampshire's Crimes Against Children Research Center also found that 34% of Internet users between the ages of 10 and 17 posted real names, telephone numbers, or addresses. Forty-five percent posted their real ages, according to the researchers.

"The Internet is one of the greatest technological advances of our time, but it also makes it alarmingly easy for sexual predators to find and contact children," U.S. Attorney General Alberto Gonzales said in a prepared statement. "The Think Before You Post campaign sends a strong reminder to children and their parents to be cautious when posting personal information online because anything you post, anyone can see: family, friends, and even not-so-friendly people."

The online game ID the Creep challenges young people who think they would be able to identify a predator to play along and see how they score. It allows "players" to engage in simulated chat, e-mail, and IM situations and choose from several statements as they reply to others, and then it rates how they did.

Another part of the campaign features public service announcements to inform young people that networking sites and blogs are public and information within them can be obtained by anyone. They also urge people to check the National Center for Missing and Exploited Children's tip pages for preventing and reporting online sexual exploitation. Similar campaigns have focused on informing adults about risks and how to communicate dangers to teens.