Parents were warned today of the dangers of explicit emails and texts being sent to their children.
More than a third of secondary school children have been sent messages containing sexual content, a survey showed.
Researchers found youngsters are being sent sex texts or "Sexts" - often by their school friends.
The messages contain images of sex acts involving young people and of youngsters - both boys and girls - exposing themselves.
Material is sent to mobile phones via texts, transferred using Bluetooth or uploaded to social networking groups.
The research, carried out by children's charity Beatbullying, found it was most often not strangers sending the images.
Seven out of 10 of the 11-18-year-olds surveyed said they knew the sender personally.
A quarter of the messages were sent by the youngster's current boyfriend or girlfriend, the study showed.
Girls are bullied into taking, and sharing, explicit pictures of themselves, the charity warned.
Chief executive Emma-Jane Cross said: "We don't want to stifle young people's sexual development but it is important that parents and schools understand the rise of sexting so together we can act to stop sexual bullying.
"Politicians must pool together organisations like Beatbullying to create an intervention and prevention task force in schools and the local community.
"This needs to be part of the solution if we are to educate our young people about the consequences of their actions and how to keep safe online as well as offline."
A spokesman for the Child Exploitation and Online Protection Centre (CEOP) said there were concerns that images, once taken, could find their way into the hands of paedophiles.
Anyone holding images of youngsters or passing them on could be breaking the law, he warned.
"As mobile phones with cameras and internet access are readily available these days - and, indeed, the increased use of Bluetooth technology - images can be shared easily and at a reduced cost between friends at school.
"If you are worried that your child may be receiving or even sending indecent images on their mobiles, you should talk to them about the consequences of their actions.
"Make them aware that, once the image has been sent, they have lost control of that image and anyone can potentially have a look at it."
Schools Minister Diana Johnson said children who were facing sexual bullying should tell a teacher.
She said: "We are committed to tackling all forms of bullying - including bullying using the internet and mobile phones, and sexual bullying.
"It is important that young people being bullied know that they can report it and that it can be stopped.
"We are supporting parents to have the confidence to engage with their children on the challenges of modern life - including sex and technology.
"We are also supporting teachers to identify and intervene as early as possible.
"We are working closely with a range of mobile phone companies, websites, ISPs, children's groups and teaching unions to try to stamp out the problem."
* Beatbullying questioned 2,094 youngsters in England.Reuse content