The average UK victim of "romance fraud" lost £10,000, according to the data, released by the National Fraud Intelligence Bureau (NFIB) and Get Safe Online as Valentine's Day approaches.
More than 2,700 online dating-related crimes were reported to the police over the 12 months from the start of November 2014 to the end of October 2015.
The actual total amount lost is thought to be much higher - as many crimes go unreported due to victims being too embarrassed.
Nearly two-thirds (64%) of all romance scams originated on dating sites, with one in four (25%) originating on social media and one in 10 (10%) being initiated via email. Some reported dating frauds also originated from contact made through dating apps.
Most (62%) victims were aged between 40 and 69 years old - with people aged in their 50s the most likely targets.
The Police National Coordinator for Economic Crime, Commander Chris Greany from City of London Police, said: "Romance fraudsters are using every method available to exploit people looking for love - including dating websites, social media and direct emails.
"These heartless criminals will specifically target those who they deem to be vulnerable and most likely to fall for their scams. Our intelligence tells us that people aged 50-59 are the most likely to become a victim of dating fraud and therefore need to be especially careful when going online in search of a partner."
Victims of fraud should report it to Action Fraud, the UK's national fraud reporting centre, by calling 0300 123 20 40 or by visiting www.actionfraud.police.uk.
All reports made to Action Fraud are reviewed by the NFIB, which decides whether they should be used for enforcement, intelligence or disruption activity.
Get Safe Online is an internet security awareness-raising initiative, supported by Government bodies, banks, building societies, payment services and retailers.
Tony Neate, chief executive of Get Safe Online, said: "The financial loss is one thing, but it's the emotional impact this sort of crime has which is severe. When someone places a lot of trust and faith in a person who they think they know, they often don't separate their emotional feelings from rationale.
"Often when victims do start to suspect something isn't quite right, they're already in deep, so it's extremely easy to ignore those little niggles of doubt and choose to trust someone - it's this factor which online criminals exploit.
"It's important to remember that it's highly unlikely anyone legitimate would ask for any kind of financial assistance for whatever reason.
"Plus, if there are any immediate doubts, speak to a family member or friend to get a second, more objective opinion. If someone is keen to take their contact off the dating site very quickly, this could be a sign that they have something to hide."
Here are some tips from Get Safe Online for safe online dating:
- Trust your instincts - if you think something feels wrong, it probably is.
- Choose a site that will protect your anonymity until you choose to reveal personal information and that will enforce its policies against inappropriate use.
- Do not post personal information, such as phone numbers, on dating sites.
- Never send money or give credit card or online account details to anyone you do not know and trust.
- Wait until you feel comfortable with someone before telling them your phone number, place of work or address.
- Be extremely wary about removing clothes or doing anything in front of your webcam that could be used against you - even if you think you know the other person.
- Use a dating site that offers the ability to email prospective dates using a service that conceals both parties' true email addresses.
- Set up a separate email account that does not use your real name.
- Pick a user name that does not include any personal information. For example, "joe_glasgow" or "jane_liverpool" would be bad choices.
- Meet for the first few times in a safe place with plenty of people around, and tell a family member or friend where you are.