The survey, commissioned by consulting and IT services provider Morse, polled 1,460 workers and found that 57% of people on average spend 40 minutes on social networking sites each week.
Morse said that this equated to just under a full working week being "wasted" each year, leading to an annual loss of £1.38bn.
Of those surveyed, more than three quarters said that their employer had not issued guidelines for using micro blogging site Twitter, which Morse said was leaving groups open to brand damage and security risks.
Philip Wicks, a Morse consultant, said: "Social media can be good for business, helping to extend ties with customers and employees, but organisations don't seem to understand that it's not being used predominantly for business but for personal use. This is a massive productivity black hole.
"Companies need to reinforce a corporate usage policy to ensure that people use their PCs responsibly and predominantly for business purposes."
The study did not take into account the positive effects of social networking use for UK businesses.