Shares of Snapchat's parent company, Snap, fell more than 8% on Thursday after Kylie Jenner tweeted that she didn't use the app anymore. Short sellers made $163 million in a single day on the stock move. Short sellers — or traders betting on a stock decline — made a whopping $163 million in a single day as Snap shares fell as much as 8.5%, according to data compiled by the financial-analytics firm S3 Partners.