Twitter, social media are fertile ground for stock hoaxes

"Apparently I have a twitter impersonator," said the hedge fund manager, adding that he had no plans "to tweet about stocks."

What set off Einhorn, founder of Greenlight Capital, was a post by a since-suspended Twitter account called @Greenlightcap that read: "The $HLF tug of war will in the end come down to who has more money to play with. I wouldn't want to be in Bill's shoes right now #TeamIcahn."

That may have misled people into thinking that Einhorn - whose infrequent tweets under @davidein tend to be about poker - was picking sides in the battle between two other big-name investors, Carl Icahn and Bill Ackman, who have opposing positions in Herbalife.

Einhorn isn't the only shortseller who has been impersonated on Twitter, which has become an important source of information for many investors. In late January, shares of Audience Inc and Sarepta Therapeutics Inc plunged following tweets that were purported to be from short-selling researchers.

"Twitter pump and dump schemes are obviously something for the market to be concerned about, even if they are just a new way for people to do schemes that have been done forever," said Keith McCullough, chief executive officer at Hedgeye Risk Management in New Haven, Connecticut. He uses Twitter and has more than 22,000 followers.

In such hoaxes, anonymous users set up accounts with names that sound like prominent market players, issue negative commentary,

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