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 87% 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, 49% of those targeted by bullies were victimised off-line, while 65% of teenagers were subjected to abuse in cyberspace.
Only 37% 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."
The study, for internet site knowthenet.org.uk, found a number of social networking sites had become "popular forums" for trolls.
Some 13% of the 13 to 19-year-olds consulted claimed they were targeted on BlackBerry Messenger, 8% said they were picked on by trolls on Bebo and 4% said they were victimised on Whatsapp.
Fewer than one in five (17%) teens said their first reaction would be to tell a parent and only 1% of those surveyed said their initial response would be to inform a teacher.
Around 34% of those who were picked on by trolls said their experiences lasted more than a month.
Knowthenet, which released the study, has now launched a "trolling hub" offering advice on how to deal with online bullying.
This can be found at www.knowthenet.org.uk/trolling.
Opinium Research consulted more than 2,000 teenagers for the study.
A Facebook spokesman said: "There is no place for harassment on Facebook, but unfortunately a small minority of malicious individuals exist online, just as they do offline.
"We have a real name policy and provide people with simple tools to block people or report content which they find threatening so that we can remove it quickly."
Links to report concerning behaviour on Facebook exist on every page of the site meaning users can report any piece of content.