FACEBOOK and Google are failing to take down scam adverts, Consumer group Which? claims.
A third of people who reported an advert to Google after falling victim to it said it was not taken down.
A quarter of Facebook users said the same, a study said.
Which? consumer rights expert Adam French backed tighter regulation.
He said: “Online platforms must be given a legal responsibility to identify, remove and prevent fraudulent content.”
Facebook, headed by CEO Mark Zuckerberg, defended its record.
The firm said: “Our security experts and AI remove this content.”
Google added: “We’re constantly reviewing ads, sites and accounts to ensure they comply with our policies.”