Children and young people feel social media sites are failing to shield them from pornography, self-harm and bullying content, the NSPCC has warned.
Four in five youngsters told the charity they felt sites are not doing enough to protect them from inappropriate and harmful imagery and messages, with Facebook and Askfm rated among the riskiest sites.
Peter Wanless, NSPCC chief executive, said the charity's survey clearly showed they do not feel protected from "upsetting, dangerous, and adult content".
"It's vital parents know about their child's online world and regularly talk with their children about how to get help if they need it," he said.
"We all know that the internet develops at breakneck speed and it can feel nearly impossible to keep up with all of the constantly changing sites, games, and apps that young people use."
The research was carried out with mobile provider O2 as part of the charity's Net Aware initiative to inform parents of the risks and issues with sites their children are using.
Of the 1,696 11 to 18-year-olds who took part, 1,380 said social media sites needed to do more to protect them from inappropriate or harmful content.
The social networks Facebook and Askfm and chat sites Omegle and IMVU were rated the riskiest by children in the study.
One 16-year-old girl reviewing Askfm said the site had "no strict controls" which led to "lots of hurtful messages being spread about people".
The youngster said she believed the damaging content "contributed to people self-harming or just feeling negative about themselves."
The study comes amid concern over children using mobiles and tablets to browse websites away from the supervision of parents or teachers.
In March, Baroness Tyler, chairwoman of the Values-Based Child and Adolescent Mental Health System Commission, told MPs that schools needed staff who are "really up to date with technology" to help protect pupils and inform parents of new trends.
However former government mental health tsar Natasha Devon told the Health and Education Select Committees that children were getting around efforts to control access online, including by by owning two or three handsets.