Young people are acting out scenes they see in online pornography and even organising abuse via social networking sites and messaging systems, the Deputy Children's Commissioner has told MPs.
Sue Berelowitz told a cross-party committee on Tuesday she was worried about the role of the internet and social networking sites in cases of child abuse.
She said she was "extremely concerned" about the role being played by the internet in enabling and fuelling abuse, and ridiculed the idea that parents could prevent access.
In one case, boys aged 14 and 15 were "summoned" via BlackBerry Messenger to the gang rape of a "very, very young girl" which lasted several days, she said.
"Boys were being called while some were raping the girl to say 'come, come, come, you can join in too' and they were arriving and elbowing each other out of the way to rape her."
One police force showed her a list of more than 1,000 girls aged between 12 and 14 whom a man in his 40s masquerading as a boy had managed to make his "friends" on Facebook.
"We have gathered quite a lot of evidence to show that there is no doubt that social networking sites can be a source of real problems for this," she said.
The report comes as a jury heard about the alleged use of Facebook in a sexual abuse trial involving a 14-year-old girl in Lancashire. The girl told police about an account created with photographs of her and accompanying messages such as "free blowjobs" and "she sucks as well".
Sue Berelowitz told MPs that easy access to extreme pornography was a particular concern.
"We've had boys say to us - some of the boys I've spoken to who've been involved in sexual exploitation - 'it was like being in a porn movie'. They have watched things and then they've enacted them.
"Parents may think they can control what's going on because they can have a blockage on the computer but the reality is children can get anything they like on their mobile phones. And they are. It has definitely affected children's thresholds of what they think is normal."
In another case, older men were using young male gang members as a "front line" in a wider abuse network, and had even forced two of the boys to have sex and filmed it on a mobile phone to ensure their compliance.
Her evidence to MPs was part of wider research Berelowitz is conducting into child sex abuse in the wake of the Rochdale grooming case.
She also revealed thousands, not hundreds, of children were being exploited across the country in metropolitan and rural areas, as well as across race and ethnicity.