The Commission analysed the policies of 22 social networking sites in a study aimed at finding out how well-protected under-18s were when using them as part of a campaign to urge young people to protect their information online.
It said that just 40% of the sites they examined had default settings which hid the personal information of minors from all but their friends and family. Just 11 of 22 sites examined stopped minors' profiles being visible to search engines.
The Commission looked at the 25 websites operated by 20 companies which signed up to its 'safer social networking principles' last year. Some of the tests were not applicable for some of the sites.
It found that sites did have some protecting measures in place. Nineteen of 23 sites examined for their safety tips did publish information targeted directly at children and young people, though it was easy to find and understand on just 14 of them.
The Commission said that 50% of teenagers give out personal information online which, according to a Commission statement, "can remain online forever and can be seen by anybody".
“If we want children to think before they post, social networking companies should post the right information using the right language," said Information Society Commissioner Viviane Reding. "I expect all companies to do more. Minors' profiles need to be set to private by default and questions or abuse reports have to receive quick and appropriate responses. The internet is now vital to our children, and it is the responsibility of all to make it safe.”
The study found that 19 of the 25 sites examined carried links through which people could report abuse or suspicious activity.
"[But] only 9 (out of 22) responded to complaints submitted during the assessment," said the Commission statement. "There is therefore an urgent need for better services to respond to users' reports asking for help."
Last year 20 companies signed up to the Commission's 'safer social network principles' which aim, in the principles' words, to "maximise the benefits of the internet while managing the potential risks to children and young people".
The Commission's report on the progress of the principles' original 18 signatories and the two which joined later said that improvements had been made to how the sites were run.
"Most of the companies empower minors to deal with potential online risks and employ a safe approach to privacy by making it easy for users to block other users and remove comments from their profiles; making privacy options easy to change so that users can choose whether only their friends or the entire world can see what they post online; [and] giving users control over the display of their online status (which allows other users to see whether they are online or not)," the Commission said.