The study, for internet site knowthenet.org.uk, found a number of social networking sites had become 'popular forums' for trolls.
Some 13 per cent of the 13 to 19-year-olds consulted claimed they were targeted on BlackBerry Messenger, 8 per cent said they were picked on by trolls on Bebo and 4 per cent said they were victimised on Whatsapp