Sarepta Therapeutics Inc became the second company in as many days to see its shares plunge as a result of a Twitter hoax on Wednesday after a user posed as an influential short-seller and alleged improprieties at the biopharmaceutical company. The drop mirrored a similar incident on Tuesday, when Audience Inc fell more than 25 percent following tweets that at a glance looked to be from Muddy Waters, another short-selling firm.