Facebook is the worst social networking site for internet trolling, and bullying is now more prevalent online than anywhere else, a study has suggested.
Some 87pc of teenagers who reported cyber-abuse said they were targeted on Mark Zuckerberg's site, while around one-fifth of youngsters were picked on by Twitter trolls, the report showed.
Those most frequently victimised were 19-year-old boys.
According to the report, 49pc of those targeted by bullies were victimised off-line, while 65pc of teenagers were subjected to abuse in cyberspace.
Only 37pc of those who had experienced trolling ever reported it to the social network where it took place, the report found.
Emma-Jane Cross, CEO and founder of the charity BeatBullying, said many young people were suffering in silence.
"Bullying both on and off-line continues to be a serious problem for a huge number of teenagers and we cannot ignore its often devastating and tragic effects," she said.
"We work with hundreds of young people being cyber-bullied or trolled so badly that it can lead to depression, truancy, self-harm, or even force them to contemplate or attempt suicide."
Media psychologist Arthur Cassidy said online bullying could have a "massive impact" on older male teenagers.
"Suicide rates are particularly high amongst this demographic, so it's worrying to hear that teenagers are choosing to deal with internet abuse themselves rather than speaking to parents or teachers," he said.
"Whilst some might expect girls to be more vulnerable online, this study shows that older boys are more at risk from trolling and cyber-bullying.
"Many boys feel under pressure to demonstrate their bravado, particularly on the web, but this attitude and male deficiency in coping strategies can make them more vulnerable and open to trolling."
The study, for internet site knowthenet.org.uk, found a number of social networking sites had become "popular forums" for trolls.
Some 13pc of the 13 to 19-year-olds consulted claimed they were targeted on BlackBerry Messenger, 8pc said they were picked on by trolls on Bebo and 4pc said they were victimised on Whatsapp.
Fewer than one in five (17pc) teens said their first reaction would be to tell a parent and only 1pc of those surveyed said their initial response would be to inform a teacher.
Around 34pc of those who were picked on by trolls said their experiences lasted more than a month.
Knowthenet, which released the study, has launched a "hub" offering advice on how to deal with online bullying: www.knowthenet.org.uk/trolling.
More than 2,000 teenagers were consulted for the study.