Bullying on the internet and mobile phones is an increasingly common problem among today's youth, according to new research.

A recent study by the US National Crime Prevention Council and research firm Harris Interactive found that more than 43 per cent of US citizens aged 13-17 have experienced cyber-bullying in the past year.

About 93 per cent of teens use social media sites, according to the Pew Internet and American Life Project, and 55 per cent of online teens have created a profile at social networking sites such as MySpace and Facebook.

But while these sites allow teens to express their feelings for the world to view, they also give cyber-bullies the opportunity to harass individuals by posting negative comments and pictures.

Just last week, a US woman was indicted on federal charges of fraudulently using a MySpace account to pose as a teenaged boy. Prosecutors allege that her actions ultimately caused a 13 year-old girl to commit suicide.

The California Association of Marriage and Family Therapists said that victims of cyber-bullying usually feel a wide range of emotions, including indifference, anger and embarrassment.

Only about 35 per cent of teens have told a parent about being bullied, and 16 per cent have told no one.

The therapist group said that parents need to be aware of cyber-bullying by monitoring teens' online activity.

Parents should encourage teens not to respond to the bullying, and should save pictures and messages as evidence.

They should also contact the school to report the cyber-bullying, block the cyber-bully from future contact and try to contact the cyber-bully's parents. If this is not possible parents should contact the police or an attorney.