One in three young Britons have been the victims of cyber-bullying with girls the most likely victims, according to research published on Tuesday.
A survey by the Beatbullying charity of more than 2,000 youngsters aged 11 to 18 said text messages, prank mobile phone calls and content posted on social networking sites were at the heart of a "growing epidemic."
Teenage girls were four times more likely to be bullied this way than boys, the research found.
"Clearly, cyber-bullying is a growing problem affecting millions of children across the UK and to date efforts to tackle the epidemic have fallen short," said Emma Jane Cross, the charity's chief executive.
The findings coincide with the launch of a new nationwide social networking site CyberMentors, backed by celebrities and politicians such as Prime Minister Gordon Brown, which allows trained schoolchildren to provide help and advice for their peers.
"CyberMentors is an exciting new initiative to help keep Britain's children and young people safe online," Brown said.
"Just as we wouldn't let them go unsupervised in playgrounds or in youth clubs, so we must put in place the measures that we need to keep our children and young people safe online."