Celebrity influencers are being used to promote crypto-currency and currency trading schemes which turn out to be scams, the City watchdog has warned.
These celebrities often have a large following on social media - an opportunity seized on by con-artists to cast a wide net for potential victims.
Bogus online trading platforms promise supersized returns but fraudsters may disappear with the invested funds.
Crime reporting centre Action Fraud said victims lost £27m in 2018-19.
The Financial Conduct Authority (FCA), the City watchdog, said that celebrity endorsements and images of luxury items such as expensive watches and cars on social media posts were often used to promote schemes.
These then linked to professional-looking websites where consumers were persuaded to invest.
However, it said that those tempted should remember not every investment opportunity is genuine. Criminals could use the names of well-known brands or individuals to make their scams appear legitimate.
Laura Suter, from regulated investment platform AJ Bell, said: "If your friend recommends something to you, don't assume that they have done all the research for you. You can check on the regulator's register to see if the company is legitimate."
Reports of either foreign currency or crypto-currency fraud more than tripled last year to 1,834 cases. The typical amount lost by each victim was £14,600.
Action Fraud director Pauline Smith said: "These figures are startling and provide a stark warning that people need to be wary of fake investments on online trading platforms. It is vital that people carry out the necessary checks to ensure that an investment they are considering is legitimate."
'I was building a new life but lost thousands'
Painter and decorator John Walker had been injured and was recovering in bed when he spotted an advert for Bitcoin trading online.
He was attracted by the low starting investment of £250 and was looking to build up some savings as he and his family embarked on a new life in Cornwall.
"Bitcoin was going crazy at the time," the 53-year-old said, so he decided to invest.
All seemed to go well, but he soon received a phone call suggesting he pump in another £5,000.
Claiming they wanted to make it all hassle-free, the operators said they could transfer money from his bank account.
In fact, they were fraudsters who, over a few days, gathered enough banking information to clear thousands of pounds from his account.
Having seen what he thought was his investment rapidly gathering value, all of a sudden the con-artists disappeared with his money. Mr Walker lost £41,000.
"You don't get something for nothing - that's the lesson," he said.
Now, on a so-called suckers list which is sold between fraudsters, Mr Walker said he received four or five scam calls every day.
The FCA has warned about such "get rich quick" schemes before, and said hype around crypto-currencies had been seized on by fraudsters.
A small minority of people have invested in this kind of digital currency. However, many of those who do have little understanding of what they are doing, the FCA says.
Owing to the lack of regulation, there is no compensation or protection for investors if things go wrong.
Last year, the Treasury Committee of MPs said that Bitcoin and other digital currencies were a "Wild West industry" which needed to be regulated to protect investors.
The legitimate crypto-asset industry has been calling for "greater certainty to protect consumers".
CryptoUK, which was set up last year as a self-regulatory body for the crypto-currency industry, wants official oversight from regulators to be introduced.