“There’s a whole group of investors who really don’t care about the inherent value of a company,” he said. “They just care if there’s someone else who will pay a higher price.”

The SEC is also likely to investigate whether users are being paid for their recommendations by companies or other organisations seeking to move a stock. Any investigation could take months — or longer — involving subpoenas of user IP addresses and broker trading records, Mr Cutler said.

The commission can also intervene sooner if it sees egregious market moves or suspects manipulation by suspending trading in a stock or by seeking temporary relief through the courts. Mr Cutler noted, though, that suspensions were often unpopular because it left investors who had jumped into the stock stuck in the shares.

The SEC declined to comment.

Options are central to retail investors’ success in moving markets, with the use of the instruments that let traders bet on the direction of stock prices being amplified by no-commission websites such as Robinhood. In aggregate, this has forced big brokers to buy stocks to hedge their own risks, helping supercharge the influence of day traders who typically have much less financial firepower than their established Wall Street rivals.