Social networks' failure to tackle cyber-bullying is risking the mental health of young people, a Children's Society survey has found.
Almost half of 1,089 11 to 25-year-olds questioned for the Safety Net report had experienced threatening or nasty social media messages, emails or texts.
Two-thirds said they would not tell their parents if they experienced something upsetting online.
However 83% want social media companies to do more to tackle the problem.
According to the Safety Net report, most of the respondents felt that there was a lack of consequences for people who engage in bullying behaviour online, in contrast to the offline world.
"Social media companies should take complaints more seriously. If someone reports something, they shouldn't take days to review it, they should literally just remove it straight away," said a 15-year-old girl, who responded to the online survey.
"The reaction from adults is just delete your account to stop the bullying, but that's taking something away from that young person's life for something that's not their fault."
The inquiry is calling on social media companies and the government to act to tackle cyber-bullying.
The inquiry is recommending that social media companies:
- Respond to reports of bullying within 24 hours
- Give young users clearer guidelines on how they should behave online
- Take tougher action on those who break the rules
It also advises the government to:
- Launch online safety lessons in schools
- Require social networks to report cyber-bullying data
How cyber-bullying works
The inquiry was set up by Tory MP Alex Chalk, together with two children's charities The Children's Society and YoungMinds.
The inquiry found that cyber-bullying takes many forms, including:
- persistent messaging
- sharing embarrassing photos or information online
- mass "unfriending" the accounts of the target being bullied
The 15-year-old female survey respondent said that young people today "kind of expect" to experience cyber-bullying.
"Nasty comments on the selfie, Facebook posts and Twitter posts, people screengrabbing your Snapchat story to laugh about it… I feel like it's something people don't take seriously," she said.
"But leaving just one nasty comment could really hurt someone."
The inquiry also found that social media is extremely addictive, with one in 10 young people surveyed admitting that they log on to social networks after midnight every night.
One respondent likened social networks to being "almost like a drug", and young people gave evidence to the inquiry that they felt judged and inadequate if they didn't have enough "likes" on posts or enough followers on their accounts.
The heaviest users of social media amongst the respondents were mostly likely to have low wellbeing and symptoms of anxiety and depression.
And those who had been bullied online told the inquiry that they would frequently check their account newsfeeds to see what else had been shared or said about them on the platforms.
"Cyber-bullying can devastate young lives, but to date the response from social media companies has been tokenistic and inadequate. It has failed to grip the true scale of the problem," said Mr Chalk.
"For too long they have been marking their own homework and it's time they become far more transparent, robust and accountable."