Coordinating Trades on Reddit Could Be Manipulation, EU Warns

The top European markets regulator delivered its strongest warning yet about the risks of using social media for investing, cautioning that any effort to coordinate trades online could violate market-manipulation rules.

The Paris-based European Securities and Markets Authority said it was acting following the frenzy in trading in U.S. companies including GameStop Corp. The trading, fueled by retail investors on Reddit message boards, has prompted investigations into potential market manipulation as well as calls for greater scrutiny of mobile trading apps, short-selling rules, broker solvency and social media.

“Discussing the opportunity to buy or sell the shares of an issuer ...