Shares in GameStop surged again, rising 74 percent at the start of trading in New York
Watchdogs in the US and UK said they were monitoring activity and potential lawbreaking, and warned traders they risked facing huge losses.
Traders should ensure they are familiar with all rules, “including market abuse”, the UK’s regulator said.
GameStop is the focus of a trading war between amateurs and Wall Street pros.
Shares in the US bricks and mortar video games retailer surged again on Friday, rising 74 percent at the start of trading in New York. Another stock in the traders’ sights, AMC Entertainment, jumped 60 percent.
That bucked broader market trends, which saw all three main US indexes fall roughly 2 percent in early afternoon trade in New York.
Some share trading firms temporarily halted dealings on Thursday amid extreme volatility in GameStop, which has soared as much as 700 percent in the past week. AMC Entertainment and Blackberry, which have also seen huge trading activity, were among the other companies also hit by the restrictions.
UK traders have also been sharing their thoughts and tips on trading chat forums amid mounting concerns about misinformation and share ramping.
London-listed companies have also been the focus of social media attention, including publisher Pearson and cinema operator Cineworld, although the share price movements were minimal compared with the GameStop surge.
In a statement on Friday, the UK’s Financial Conduct Authority said: The FCA is aware of the situation and continues to closely monitor trading in UK markets. UK investors should take care when trading shares in highly volatile market conditions that they fully understand the risks they are taking. This applies to UK investors trading both US and UK stocks.
It said that firms and individuals should also ensure they are familiar with, and abiding by, all regulations, including the market abuse and short selling regimes in the jurisdiction they are trading in.