Cryptocurrency scams are using images of celebrities and upmarket London addresses to hoodwink consumers into parting with cash, Britain's Financial Conduct Authority has said.
The warning, first made in June, was reposted on the FCA's website yesterday.
Similar scams have run here, including one that falsely claimed an endorsement from presidential candidate Gavin Duffy.
Cryptocurrencies such as Bitcoin are not regulated in Britain, and the FCA said it has received a rising number of reports about investment scams that claim to offer high returns.
"UK consumers are being increasingly targeted by cryptocurrency-related investment scams," the FCA said in a statement.
"Cryptocurrency fraudsters tend to advertise on social media, often using the images of celebrities or well-known individuals to promote cryptocurrency investments."
The ads link to websites for investments either using cryptocurrencies or traditional cash.
"The firms operating the scams are usually based outside of the UK but will claim to have a UK presence, often a prestigious City of London address," the FCA said.
Given that cryptocurrencies are not regulated, affected consumers are unlikely to get their money back, and are not protected by the Financial Services Compensation Scheme, the watchdog said.
In April this year, Gavin Duffy told RTÉ's 'News at One' that his image was used without his knowledge or permission in an advertisement for a scheme called Bitcoin Trader.
The ad was presented as a news report about Bitcoin Trader being endorsed by stars on an episode of Dragons' Den, and included a false testimonial from Mr Duffy.
The testimonial claimed the Dragons had made a huge financial return by using Bitcoin Trader.
On RTÉ, Mr Duffy said he initially thought the ad, versions of which continue to be seen on websites including Facebook, was "silly" but issued a statement because he was concerned that people would be taken in by it and lose money."
(Additional reporting Reuters)