And fake ads have been waved through by Google and Facebook without proof of authenticity, signatories of the letter claim.
They said the internet giants should have a legal obligation to stop fraudsters misusing advertising platforms and for this to be included in the forthcoming Online Harms Bill.
At the moment financial fraud is not covered by the legislation, which largely focuses on child safety, bullying and extremist content.
More than £78million was lost to brand cloning scams last year – or an average of £45,000 per victim – according to Action Fraud.
Victims are often elderly people who are approaching or in retirement and the devastating losses can mean they are forced to work longer or sell their home.