Almost one in five children in the UK who use social networking sites suffered a negative experience, including bullying, unwanted sexual messages, cyber stalking last year, research by a children's charity has found.
The National Society for the Prevention of Cruelty to Children (NSPCC) also said a large number of users of Facebook, Twitter and YouTube in the country were under the minimum age of 13.
The survey also showed that the most common bad experiences among children were bullying and trolling.
This involves insulting or intimidating others, usually under a pseudonym, to provoke a reaction.
The NSPCC said the survey was commissioned because of increased concern around what children and young people were being exposed to on the Internet.
Earlier this month, 14-year-old Hannah Smith, from Leicestershire, was found hanged. Her father said she had been sent abusive messages on a social networking site.
Claire Lilley, NSPCC safer technology expert, said: "It's unbearable to think any young person should feel there is no other option but to end their life because of bullying on social networking sites."
She said their research revealed a "worrying landscape" and the charity's forthcoming report would focus on the issues of "trolling" and cyber-bullying and the impact they have on young children.
"This is something that must be tackled before it gets out of hand," the BBC quoted Lilley as saying.
"We must ensure young people have the confidence to speak out against this abuse, so that they don't feel isolated and without anywhere to turn."
Last week, Prime Minister David Cameron asked people to boycott websites that fail to tackle online abuse.
"The people that operate these websites have got to step up to the plate and show some responsibility in the way that they run these websites.
"Just because someone does something online, it doesn't mean they're above the law. If you incite someone to do harm, if you incite violence, that is breaking the law, whether that is online or offline.
"Also there's something all of us can do as parents and as users of the Internet and that is not to use some of these vile sites. Boycott them, don't go there, don't join them - we need to do that as well. I'm very keen we look at all the action we can take to try and stop future tragedies like this," Cameron had said.
