More than a million young people in Britain are subjected to extreme online bullying every day, according to the biggest survey of internet abuse.
The explosion of social networking sites means seven out of 10 people aged 13 to 22 have been cyber-bullied, a survey by the national anti-bullying charity Ditch The Label has found.
The growing problem now affects an estimated 5.43 million young people, with girls and boys equally likely to be targeted. Facebook was the most common place for it to occur, with young people twice as likely to be bullied there than on any other social network.
More than half of its users said they had been victimised on the site at some point, compared with 28 per cent of Twitter users and 26 per cent of those on Ask.fm.
More than 10,000 young people were asked about their experiences of abuse over the internet and asked to rate its severity. One in five said they experienced bullying every day at a level that they rated eight or more out of 10.
Liam Hackett, who founded Ditch the Label after being a victim of bullying himself, said: "Historically bullying went on in the classroom and it stopped when you got home, but now there's no escape for young people."
He added: "Cyber-bullying is seriously damaging the self-esteem and the future prospects of young people and is an issue we cannot afford to overlook. Social networks have a moral obligation and a duty of care to their users to implement tight mechanisms of flagging and reporting systems for cyber bullying, although we all have a responsibility and an opportunity to help fix this."
The results follow the deaths of two teenagers over the northern summer who were bullied over the internet. Hannah Smith, a 14-year-old schoolgirl was found hanged at her home in Lutterworth, Leicestershire, after apparently suffering months of internet abuse on social network Ask.fm.
Daniel Perry, 17, from Dunfermline, Fife, killed himself after footage recorded on Skype was used to blackmail him.
Helen Goodman, shadow minister for culture, media and sport, with a responsibility for media reform, said: "Cyber-bullying is a horrible new problem facing some of our teenagers. It is vital that adults, including companies and the Government, take responsibility for making sites safe."
She added: "We have repeatedly called on the Government to introduce legislation to deal with this epidemic of cyber-bullying, but [Prime Minister] David Cameron is failing to stand up to the internet giants."
Ditch the Label believes the Government needs to make social networks more thoroughly regulated to protect young people from abuse.
Hackett said: "There needs to be greater governance of social networks. Especially with the likes of Facebook and Twitter, we feel there should be greater legal obligation to do an annual external audit which would tell us how much abuse had been reported and what the response had been."
The children's counselling service ChildLine is appealing for more volunteers to help work on its online support team as it struggled to cope with the demand.