An ICO website aims to help young people protect personal details
The Information Commissioner's Office found more than half of those asked made most of their information public.
Some 71% of 2,000 14 to 21-year-olds said they would not want colleges or employers to do a web search on them before they had removed some material.
The commission said the young needed to be aware of their electronic footprint.
The ICO also said young people could be putting themselves at risk of identity fraud because of the material they post on social networks such as Facebook and MySpace.
Information Commissioner's Office
The data regulator's survey found that two thirds of those questioned accepted as friends on such websites people they did not even know.
Some 60% posted their date of birth, a quarter put their job title and almost one in 10 gave their home address.
ICO deputy commissioner David Smith said: "Many young people are posting content online without thinking about the electronic footprint they leave behind.
"The cost to a person's future can be very high if something undesirable is found by the increasing number of education institutions and employers using the internet as a tool to vet potential students or employees."
The survey found 95% were concerned about their details being passed on to advertisers or other websites.
There were 54% who cared "a lot" about how their personal information was used.
Mr Smith said: "This shows that when young people are made aware that their details could be being passed between parties - legitimate or unscrupulous - they are worried.
"We have to help teenagers wise up to every aspect of the internet age they're living in. It may be fun but unfortunately it is not the safe space many think it is."
The ICO has launched a new website to help young people understand their information rights.