Around 80% of young people think social media companies should do more to tackle cyber bullying, according to a study.
Almost half have experienced threatening, intimidating or nasty messages and 14% have been a victim of online bullying in the last month, research by YoungMinds and The Children's Society found.
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.
"As a society we are in the foothills of our understanding of the impact of social media on young people's mental health.
"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.
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.
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.
"But we're also excited to see how this inquiry can work with social media companies to find innovative ways to promote mental health among young people, empowering them to understand how to respond to what they see online and cope with the pressures that social media brings."
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.
"The parliamentary inquiry will give us the opportunity to hear more from experts, young people and social media companies about how young people can be better protected from these negative experiences.
"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."
The results of the inquiry are due to be published in a report early next year