by: Douglas MacMillan | BusinessWeek

Groupon Inc. (GRPN) plunged to a record low after the largest daily-deal website reported second-quarter revenue that missed estimates as economic weakness in Europe curbed online coupon sales.

The shares retreated 23 percent to $5.80 at 9:43 a.m. in New York, and earlier touched $5.76 for the biggest decline since the company’s initial public offering in November.