Such companies offer a wide variety of unmoderated matchmaking services, most of which are profile-based.
That could allow anyone to extort Adult Friend Finder customers.
Tinder proved more popular among girls than boys, with one in five female respondents using it compared with 15% of males, according to the poll of 2,000 11 to 17-year-olds and 2,000 parents by Internet security firm Mc Afee.
Four in 10 said they had witnessed others being picked on online - almost double the 22% recorded last year.
Less than a third of parents (27%) said they were worried about their child being the victim of cyber-bullying this year - almost halving from 45% in the previous year, while two-thirds (67%) of children are now allowed to go online without supervision - up from 53%.
There is no requirement for authentications or credentials to access it.