Almost half of young people have experienced threatening, intimidating or nasty messages online, a study found.
Of these 14% said they had been a victim of cyber bullying, according to a survey by YoungMinds and The Children's Society.
It comes as 80% of young people said social media companies should do more to tackle online abuse.
Many said their personal information had been shared publicly, they had been excluded from conversations or groups online or received persistent messages from someone after asking them to stop.
The survey of around 1,000 people aged 11-25 was carried out ahead of an inquiry in Parliament into the impact of cyber bullying on young people's mental health.
Conservative MP Alex Chalk, who is leading the inquiry, said: "Social media is a good thing, but there is increasing evidence that prolonged exposure at such a young age carries risks.
"This robust, evidence-based inquiry will improve our knowledge and help young people more safely navigate what can feel like a minefield."
A panel will hear from young people, experts and social media companies on what can be done to tackle cyber bullying and promote good mental health.
Around 40% of those polled said social media had a negative impact on how they feel about themselves.
And almost 60% admitted having accounts when they were below the minimum age of 13.
Despite the findings, 60% of young people said social media had a positive effect on their friendships.
Matthew Reed, chief executive of The Children's Society, said: "The fact that young people themselves are saying social media giants must do more should be seen as a wake-up call.
"Social media can bring many benefits and it's so important that young people can enjoy using it without it damaging their self-esteem or mental health."
Sarah Brennan, chief executive of YoungMinds, said: "Young people must feel safe online, and more needs to be done to prevent and respond to cyber bullying when it happens."
The results of the inquiry are due to be published in a report early next year.