Almost one in five 11- to 16-year-olds have suffered a bad experience on the Internet in the past year.
The study of 1,024 children revealed that bullying and trolling were the most common but many had also been subjected to unwanted sexual messages and being pressurized too look a certain way.
The NSPCC also said a "large number" of users of Facebook, Twitter and YouTube were under the minimum age of 13.
The news comes after 14-year-old Hannah Smith was found hanged earlier this month after she was abusive messages on social networking site, ask.fm.
Claire Lilley, NSPCC safer technology expert, told the BBC: "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."
"This is something that must be tackled before it gets out of hand," she said.
"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."
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Last week, Prime Minister David Cameron called on people to boycott websites that fail to tackle online abuse in response to Hannah Smith’s death.
