How about the ~opposite: you tweet something to move the stock price but you don't make any trade? It you have access to insider information this is a Reg FD violation as others have written. But what if you have no insider information? You just make something up and use your social media influence to manipulate stock prices -- for personal reasons, political reasons, or just for fun. I would assume this is also illegal, but can't recall any specific law or precident.