"First, retail trading forums and social platforms have once again become engines of crowd momentum," she wrote. "Second, these stocks are all heavily shorted, setting the stage for violent short squeezes when buying pressure ramps up."

Shares in a donut chain, camera company and meat-substitute maker surged Wednesday in a revival of meme stocks. Krispy Kreme, the North Carolina-based chain with about 350 shops, soared as much as 25% on Wednesday. GoPro, famous for its miniature action cameras, jumped 49% while Beyond Meat rose 11%.

Shares in Krispy Kreme donuts, camera maker GoPro, and retailer Kohl's have risen dramatically this week, driven by online hype.