More than half of online dating app and website users believe they've seen a fake profile with two in five having been approached by someone asking for money.
The Which? survey of 1,000 users of online dating services also found that one in seven admitted to sending money to someone who had asked for it.
Of those who sent money, men were twice as likely to have parted with cash when asked to than women.
Usage of dating website and apps is on the rise, which means that potential for fraud is also rising.
Of the dating sites used by those surveyed, users of Lovestruck.com were more likely to be asked for cash with more than a third reporting they'd been approached for money while using the site.
Almost three in ten users of Dating Direct and Elite Singles also reported that they'd been approached for money while on these sites.
The Which? survey also found that around six in ten people had seen what they believed to be a fake profile.
Tinder was revealed to be the dating app where most people thought they had encountered a fake profile, closely followed by Plenty of Fish and Lovestruck.com.
But only three in ten said they reported fake profiles when they saw one.
Which? director of campaigns Alex Neill said: 'It's important for people to be vigilant when using dating sites or apps and ensure they are not revealing personal data that then could be used by scammers.
'We've found most dating sites are quick to act on reports of fake profiles and scam attempts, so we encourage anyone who sees a fake profile or is approached by a suspected scammer to report it.'
During this investigation, Which? heard from Deborah*, who reported that she'd lost £4,000 to a dating scam last year in what she described as a 'horrid situation' that caused considerable distress.
Deborah met Steven while using Encounters Dating. He presented himself as a business consultant working in the oil industry who was often out of the country.
After a few weeks of regularly speaking through online messaging, email and a couple of telephone calls, they arranged to meet.
A matter of hours before the couple were due to meet face to face for the first time, Steven messaged Deborah to say he was out of the country and in desperate need of cash to fulfil a business contract.
Deborah initially refused to send money, insisting that Steven must know someone else who could help.Steven pushed harder, becoming frantic and desperate saying she was the only one who could.
Despite her misgivings, Deborah succumbed to the pleas of a man with whom she believed she shared a mutual affection and transferred the funds to Steven.
Shortly after making the transfer, Deborah confided her concerns in a friend who warned her this could be a scam. Despite making several attempts to stop the payment, it went through.
Deborah's bank said it had no reason to stop the payment - she had authorised it.
After reporting the scam to the dating site, the offending profile was immediately removed, but Deborah was still left £4,000 out of pocket.
Users of online dating websites need to be alert to the potential for fraudulent activity. To guard yourself against being scammed,follow our tips:
*Please note that names and some minor details have been changed to preserve anonymity.