One in five young people has been a victim of cyber-bullying, which experts warn can cause more psychological damage than traditional bullying.
Hate emails, threatening texts and humiliating images posted on social networking sites are twice as likely to be targeted at girls rather than boys, according to research by Anglia Ruskin University (ARU).
Cyber-victims can suffer more because they feel unable to escape from online and mobile phone threats. The hidden identities of cyber-bullies as well as the ability for messages and images to "go viral" within minutes, amplifies the threat, said Steve Walker, the study's co-author and principle lecturer in child and adolescent mental health at ARU.
The ARU survey of nearly 500 10- to 19-year-olds found that half of those bullied said their mental health had suffered as a result. More than a quarter had missed classes and more than a third stopped socialising outside school.
The online survey was followed by two focus groups which analysed in more depth the experiences and fears of 17 youngsters in London and Leeds.
Walker said: "They cannot come home from school, shut their bedroom door and feel safe, because as soon as they switch on the computer or receive a text, the potential is there. It is much harder to avoid than traditional bullying because avoiding the internet and mobile phones just isn't an option; these are as much part of a young person's life as brushing their teeth."
He added: "Anti-bullying campaigns and professionals working with young people need to be smarter and more in tune with technology so they pick it up, because cyber-bullying poses a serious public health problem."
Research by Beatbullying found cyber-victims were often targeted in person as well. However, Richard Piggin, Beatbullying's deputy chief executive, said perpetrators tended to underestimate the impact of cyber-bullying because they could not see the distress they caused.