The number of victims of identity theft rose by 57% last year, figures from fraud prevention service Cifas suggest.
The data, taken from 261 companies in the UK, suggests fraudsters are increasingly getting people's personal information from social media sites.
Cifas said Facebook, Twitter and LinkedIn had become a "hunting ground" for identity thieves.
It said there were more than 148,000 victims in the UK in 2015 compared with 94,500 in 2014.
A small percentage of cases involved fictitious identities but most fraudsters assumed the identity of a real person after accessing their name, date of birth, address and bank details. More than 85% of the frauds were carried out online.
Some personal details were found by hacking computers but increasingly fraudsters used social media to put together the pieces of someone's identity, Cifas said.
It urged people to check their privacy settings and think carefully about what information they share online.
The Get Safe Online campaign warns people not to give away details such as phone numbers, addresses or date of birth, or pictures of their home, workplace or school, in either profile information or posts.
Often victims did not even realise they had been targeted until a bill arrived for something they did not buy or they experienced problems with their credit rating, the fraud prevention service added.
How to protect yourself and social media
A report out earlier this year estimated the annual cost of fraud in the UK was £193bn - equal to nearly £3,000 per head of population.
Business fraud accounted for £144bn, the study said, while fraud against individuals was estimated at £9.7bn.
Simon Dukes, Cifas chief executive, said: "Fraudsters are opportunists. As banks and lenders have become more adept at detecting false identities, fraudsters have focused on stealing and using genuine people's details instead.
"Society, government and industry all have a role in preventing fraud. However, our concern is that the lack of awareness about identity fraud is making it even easier for fraudsters to obtain the information they need.
"The likes of Facebook, Twitter, LinkedIn and other online platforms are much more than just social media sites - they are now a hunting ground for identity thieves.
"We are urging people to check their privacy settings today and think twice about what they share. To a fraudster, the information we put online is a goldmine."