SIOUX FALLS, S.D. - The message of a new ad campaign is that Internet social networking sites are also a hangout place for sexual predators, so teens should not post photos of themselves.

Marty Jackley, U.S. attorney for South Dakota, said his office and other law enforcement agencies in the state have joined an effort started by the U.S. Justice Department called Project Safe Childhood.

"The primary goal is to make teenagers and parents aware of the fact that when a teenager posts a picture on MySpace or another area, it's essentially going out to the whole world," he said. "You can't take it back once you posted it."

Investigators are seeing more incidents of sexual predators making contact with children over the Internet, Jackley said.

One such case pending in U.S. District Court in South Dakota involves a former North Dakota part-time library clerk charged with traveling south to have sex with a 15-year-old girl.

David Boschee, 38, of Bismarck, N.D., pleaded not guilty to that charge and a second count of using the Internet to entice a child to engage in unlawful sexual activity.

He and the girl both had profiles on MySpace.com and communicated through it, according to an affidavit filed in court.

The new South Dakota ad campaign includes newspaper, television and radio ads, Jackley said.

Another goal of the project is to let potential predators know the consequences of having, sending or making child pornography are steep, Jackley said.

Possession carries a maximum punishment of 10 years in prison. Transferring child porn has a punishment range of five to 20 years. And a conviction for manufacturing child porn is punishable by 30 years to life in prison.

Studies indicate a strong connection between someone viewing child porn and a likelihood of molesting a child, Jackley said. By cracking down on child porn users, authorities cut its supply, he said.

"It's a desire to shut down that demand so there isn't any financial gain or reason for predators to supply children pornography," Jackley said.