Research from anti-bullying charity Ditch the Label suggests social media is making youngsters more anxious.
40% said they felt bad if nobody liked their selfie and 35% said their confidence was directly linked to the number of followers they had.
One in three said they lived in fear of cyber-bullying, with appearance cited as the most likely topic for abuse.
One expert said children were growing up in "a culture of antagonism".
The survey, of more than 10,000 young people in the UK aged 12 to 20, suggested that cyber-bullying is widespread, with nearly 70% of youngsters admitting to being abusive towards another person online and 17% claiming to have been bullied online.
Nearly half (47%) said they wouldn't discuss bad things in their lives on social media and many offered only an edited version of their lives.
Cyber Bullying One Of The Biggest Challenges
"There is a trend towards people augmenting their personalities online and not showing the reality," said Ditch the Label's chief executive Liam Hackett.
It found that Instagram was the vehicle most used for mean comments.
Mr Hackett said: "Cyber-bullying continues to be one of the biggest challenges facing young people.
"Not only is the internet redefining the climate of bullying, but also it is having clear impacts upon the identity, behaviours and personality of its young users."
He called on social networks to put more resources into policing the comments people post online and responding to complaints in a more timely manner.
His views were echoed by Anne Longfield, the children's commissioner for England, who also called for a government ombudsman to be set up to mediate between the social network firms and children who are having problems.
She also called for "compulsory digital citizenship classes" in schools.
More information on dealing with cyber bullying can be found here.