Researchers Janis Wolak, David Finkelhor, Kimberly Mitchell and Michele Ybarra of the Crimes Against Children Research Center at the University of New Hampshire say most online sex offenders are adults who target teens and seduce victims into sexual relationships.

They take time to develop the trust and confidence of victims, so that the teens see these relationships as romances or sexual adventures, the researchers said in a statement.

In spite of public concern, the study found social networking sites such as MySpace and Facebook do not appear to increase the risk of youth being victimized by online predators, but talking online about sex to unknown people increases vulnerability, the study says.

The findings are based on three surveys -- two telephone interviews of a combined 3,000 Internet users between the ages of 10 and 17, one in 2000 and the second in 2005 -- and one involving 612 interviews with U.S. federal, state and local law enforcement officials from October 2001 to July 2002.

The findings are published in the journal American Psychologist.