So-called "romance crimes" are when scam artists pose as people on online dating sites or apps, building a person's trust before asking for financial favours.
Police in Yorkshire say the crimes are on the rise, with the biggest concern being that victims are often convinced they are in genuine relationships, refusing to believe they are being scammed until it is too late.
Victims have lost thousands – and even their lives – to the scams.
A woman from West Yorkshire revealed to media last year how she was scammed out of £40,000 through a dating site by a man claiming to be a businessman from London.
Di Pogson, from Holmfirth, told ITV's This Morning she had signed up to a site after being widowed, striking a relationship with a man who later asked for money for an operation on his dog. Five people were jailed in August over the crimes.
And an inquest in 2010 heard how a man from Grimsby took his own life after being conned out of £82,000 by a woman he met online, leading him into insurmountable debts.
Andy Fox, who is North Yorkshire Police's Financial Abuse Safeguarding Officer, said he has seen people scammed out of tens of thousands by criminals masquerading online as loving partners.
"These things take longer to be reported because often people don't even realise they are victims," he said.
"It's very rare that the person who reports a romance scam is the victim themselves because they believe they are in a proper relationship, it's usually a relative that raises their concerns or a bank after seeing mysterious transactions."
This has been echoed by Humberside Police's Sergeant Ben Robinson, from the force's economic crime unit, who said one victim he worked with went as far as putting her house on the market to pay her online lover, with suspicions raised by someone carrying out work in her home who overheard her talking.
"Twice we managed to cancel the sale," he said.
"We went to the house so many times trying to convince her, showing her stories of other people this had happened to."
Andy Foster, South Yorkshire Police's Fraud Protect Officer, said the crime was an "emerging trend" in the region with the biggest difficulty being in tracking the criminals down.
"These scammers are totally heartless and prey on victim's sympathies or desire for love and attention. Sadly, they are also extremely difficult, if not impossible, to track down."
Sgt Robinson said that Humberside Police saw people lose £600,000 to romance crimes in the 2018-19 financial year, with the sum exceeding that between April and December last year alone.
Very often, criminals will pretend to be military personnel, high-flying business people or to live abroad, police say, so that they have excuses not to meet up with the person.
The current coronavirus pandemic and subsequent social distancing restrictions meanwhile may provide scam artists with the perfect excuse not to meet up with victims.
Mr Fox said: "The person will play on emotional heartstrings – I see it all too often. For example, one of the most common scenarios we find is the scammer will claim to be an Army official serving in Syria or Afghanistan, which would be an excuse to disappear for a few days if they say there is no WiFi or they have been on a mission.
"They will use emotional manipulation, such as saying, 'my daughter has been injured after falling off her bike and we need money for the operation', or that they need the air fare to see family, with the promise of reimbursing the victim.
"The end promise is of course that, 'I will come back to the UK and we will marry and have a life together', which of course never happens. Before the victim knows it, they have been scammed out of thousands, sometime tens or hundreds of thousands."
Mr Fox added that months or even years may pass before victims wise up, adding, "it can be incredibly frustrating".
"I have seen it all, people who are convinced they are in relationships with Katy Perry, Rihanna, even the Prince of Dubai. I have even seen someone scammed through using a Scrabble-type app."
Vigilance has now been urged more than even during the current pandemic, with the potential for more people to turn to dating sites if they are experiencing loneliness while at home.
Elderly people are particularly vulnerable, as Sgt Robinson added they were statistically "more likely to lose large sums of money".
Relatives have been warned to raise any suspicions either with their local police force, or through Action Fraud.
Mr Fox added: "If it sounds too good to be true, it probably is. People need to be aware of the signs – what is the profile like? Can you do a reverse image search of the picture? The likelihood is, if you're a 65-year-old man talking to a page three model, or a 75-year-old woman talking to a 35-year-old Army officer, that person may not be who they say they are."