Washington - US parents are keeping a close eye on their teens' activities on Facebook and other social networks, provoking a "mixed" reaction from the youngsters, a new study showed on Tuesday.The Pew Research Center's Internet & American Life Project survey found parents are taking steps to monitor such online activities amid a range of fears, including interactions with strangers and tracking by advertisers.The study, done in collaboration with the Berkman Center for Internet & Society at Harvard University, noted that 80% of parents whose teens use social networks are themselves users of social media."Some youth seem to prefer not to friend their parents," the study said. "They friend them only because it's expected of them."But the researchers found that other teens "have a positive attitude about being friends with their parents". Sandra Cortesi of the Berkman Center said teens have "mixed feelings about being friends with their parents" on social networks like Facebook."Some teens like the fact that they are friends with their family members," she said.Access to information"Other young users prefer not to friend their parents, but do it anyway because it is expected from them. And yet others keep their profiles secret or restrict parents' access to information."Some 50% of parents using social networks have commented or responded directly to something that was posted to their child's profile or account, the researchers said.The survey suggests parents are monitoring teen online activity because of persistent fears about a number of risks.While about 53% of parents said they were "very concerned" about how their child interacts online with people they do not know, 46% felt the same way about how much data is collected by online marketers tracking the activities of teens online.Parents also were concerned that activities on social networks may damage the children's reputation, and possibly come back to haunt them later in life.Two-thirds said they were worried about how their child manages his or her reputation online.RisksMary Madden, a co-author of the report, said: "Parents are anxious about a wide range of online risks for their children, but it is particularly striking that their current level of worry about data collection by advertisers meets or exceeds other concerns about their child's online activity."The researchers found 59% of parents of teen users of social networking sites have talked with their child because they were concerned about something posted to their profile or account.While nearly four in 10 such parents have helped their child set up privacy settings for a social networking site, 50% have used parental controls or other means of blocking, filtering, or monitoring online activities.And 42% have searched for their child's name online to see what information comes up about him or her.The report was based on a phone survey of 802 parents and their 802 teens aged 12 to17, conducted between 26 July and 30 September.