Figures obtained by Quilter under a Freedom of Information request found in 2019, nearly 400 pension fraud reports were submitted to Action Fraud but only 26, little more than two a month, were handed to the police.
But it is unclear how many, if any, of those investigations led to a criminal justice outcome, Quilter said.
The figures showed that for 2020 so far, 161 pension fraud reports were received by Action Fraud but only 24 have been passed on to police.
Jon Greer, head of retirement policy at Quilter, said scammers were getting away with their crimes because it was so hard to investigate and prosecute pension scams.
He said: “Pension scams and other investment frauds are extremely complex, they can span multiple jurisdictions, and can often go uncovered for years before the victim realises their money is gone.
"This all makes investigating the scams incredibly time consuming and expensive, which is why the police have to prioritise those few cases where they have a chance of success."
He added: “The legal deterrent appears to be ineffective, so more must be done to prevent scammers from operating, and to do this we must cut the line of communication between the scammers and their victims: search engines and social media.”
Quilter has called on the government to introduce measures to tackle some of the ways in which scammers target their victims online.
This could be done by including scam adverts, fake websites and other financial harms within the scope of the Online Harms Bill, which was due to be introduced to Parliament next year but no firm commitment has been made by the government.
By doing this, search engines and social media platforms would have a legal duty to remove suspected scam adverts immediately and improve their due diligence process so that it becomes harder for scammers to market investment products using paid adverts, Quilter said.
The Financial Conduct Authority spent more than £300,000 in the first half of this year fighting fraudulent and misleading adverts online. But the campaign ended in June after six months.
Mr Greer said progress on the regulation of search engines and social media platforms has been “painfully slow and the regulation has failed to keep up with the evolution of scammers”.