Research by mobile phone experts Recombu revealed a "worrying" trend of people opening up their lives to strangers online.
According to the survey of 2,000 people conducted in February, 2012 by OnePoll, 75% of Brits have accepted a friend request from someone they don't know on Facebook.
Some 82% of Facebook users were found to speak to 25 or fewer of their Facebook friends on a regular basis.
The global average for the number of Facebook friends is 190, but the average 22-year-old has closer to 1,000 online friends, according to official data from Facebook.
Britain was also revealed to be a nation of "friend cullers", with 71% of respondents admitting to regular culls of their online friends, including almost one in five (18%) deleting 'friends' every month.
The survey found that 65% of people have lied on Facebook and Twitter, and 12% have uploaded fake photos online.
Hannah Bouckley, the editor of Recombu.com, said it is "really worrying" to see people opening up their lives to strangers on Facebook.
"It seems that people who use social network sites like Facebook are in a permanent cycle of adding and deleting friends," she said.
"It has become very important to some people to have as many friends as possible, which in some cases means opening up their life to strangers, which is really worrying.
"People need to think carefully before socialising with people they don't know as more and more of our personal information is easily available online."
In March, Facebook users were warned that criminals are creating networks of fake online profiles as a way to target individuals and their homes.
Recombu's research also revealed that the majority of Brits do not know 11% of the contacts on their mobile phone address book.