Spike in Groupon shares sparks probe NEW YORK, May 18 (UPI) -- Stock market regulators said they would investigate a spike in Groupon Inc. stock, which jumped 18.5 percent Monday, sources told The Wall Street Journal. Groupon's trading volume jumped to 16.5 million shares in the day, well above its normal level, and share values dashed higher, climbing from $9.90 per share on May 11 to $11.74 per share on Monday, May 14, The Chicago Tribune reported Friday. Groupon declined to comment on the matter but the Journal said that, while the Financial Industry Regulatory Authority was looking into the sudden spike, it hadn't requested the Securities and Exchange Commission also review the trading abnormality. Groupon has announced that its first quarter revenues surged in the first quarter, up 90 percent compared to the same quarter a year earlier to $559.3 million. Concurrently, its losses were trimmed from 48 cents per share to 2 cents per share. Groupon's share prices settled down Friday, easing back 5.4 percent, the Tribune reported.