Investors see a warning in Andrew Left's conviction Andrew Left was found guilty of 13 counts of securities fraud. Bloomberg/Getty Images Monday's conviction of short-seller Andrew Left — for trades he made after using social media to publicize his market-moving reports on companies — brought a swift reaction from other investors and financial analysts. "The conviction establishes precedent that social media commentary from influential investors may constitute criminal market manipulation," the financial intelligence firm Fazen Markets wrote in a report. "Regulatory scrutiny will likely increase for prominent short sellers," it added. "Publicly traded companies targeted by activist short campaigns may experience reduced pressure as critics exercise more caution." Read more coverage from the trial Activist short-sellers like Left have been credited with exposing fraud and mismanagement as they bet a company's stock will fall.…