( CNN ) -- A new study finds that 54 percent of teens talk about behaviors such as sex , alcohol use , and violence on the social networking giant MySpace -- presenting potential risks even if all they 're doing is talking , researchers said Monday . Do you know what your teen has posted on social networking Web sites ? The study looked at MySpace profiles of 500 people who identified themselves as 18-year-old males and females in the United States . References to risky behaviors included both words and photos , the authors said . Not all teens who write about risky behaviors in their profiles actually engage in them in real life , said Dr. Megan Moreno of the University of Wisconsin School of Medicine and Public Health , one of the authors of the study , which appears in the January issue of Archives of Pediatrics & Adolescent Medicine . They may instead talk about sex , substance use , or violence because they are contemplating doing those things , or because they want to brag without actually doing what they say , Moreno said . Even if teens have not actually engaged in risky behaviors but merely brag about them online , this can still affect their future behavior , said study co-author Dr. Dimitri Christakis , professor of pediatrics at the University of Washington and director of the Center for Child Health , Behavior and Development at Seattle Children 's Hospital . Those who lie about the behaviors to show off may receive positive feedback from others -- comments such as `` that 's great '' or `` I do the same thing '' -- that encourage them to actually try out the behaviors , he said . Apart from that , teens who claim such behaviors are more likely to be victims of bullying and unwanted invitations for sex , he said . In a second study , Moreno and colleagues identified 190 profiles of 18- to 20-year-olds that contained three or more references to sexual behaviors or substance abuse . The authors then made a profile of their own , called `` Dr. Meg , '' from which they sent a single e-mail to half these profiles , warning them about the risky information and offering information about clinical resources . They found that , after three months , 42.1 percent of the profile owners who received the e-mail -- and 29.5 percent of those who did not -- either removed references to risky behaviors or made their profiles private . `` It 's really not that MySpace is bad or good . I think the lesson is that it 's a tool , and how you use it determines the kinds of outcome you 're going to get , '' Moreno said . Experts say the bottom line is that parents should get more involved in the online lives of their children . `` I tell parents that they should absolutely create their own MySpace and Facebook page , '' Christakis said . The study inspired him to create his own Facebook account , and his 10-year-old already wants to know about his `` friends , '' he said . In some cases , parents should even have their children 's passwords for these social networking sites , especially when the children are around age 13 or 14 , said Vivian Friedman , child-adolescent psychologist at the University of Alabama at Birmingham . Friedman was not involved with the study , but she is well aware of the problem . One of Friedman 's patients , the daughter of a preacher , posted nude photographs of herself online , a move that cost her father his job , Friedman said . But she said 54 percent as a figure for profiles with risky behaviors seems too high , given that most of what happens on social networking sites is `` chit-chat . '' `` I have parents that catch their kids bragging about something on MySpace , and when you actually confront them , the kid says ' I really was n't doing it , ' and they can prove they were not at the party where they were supposed to have been drinking , '' she said . Beyond keeping a watchful eye on risky interests and pictures , parents should also use social networking sites such as MySpace -- which had about 120 million users as of this summer -- as an opportunity to learn about their childrens ' favorite movies and hobbies , as well as their top friends , she said . `` You so often hear parents say ' I do n't even know my kid anymore . ' Here 's a very easy tool to get to know your kid again , '' she said . , .
Study : 54 percent of MySpace profiles of 18-year-olds mentioned risky behaviors . Authors looked at 500 randomly chosen Web profiles from U.S. teens . Many teens took down content or made profiles private after e-mail warning . Experts : Parents should know what their children are doing online .