EUROPE FRONT AND CENTER: The European Central Bank promised to take more action to tackle the continent's debt crisis. But investors in the U.S. and Europe sent stocks down, because they'd been hoping for a more detailed, immediate plan.

KNIGHT'S NIGHTMARE: Knight Capital Group, the trading firm whose technical glitch briefly caused trading chaos Wednesday, lost 63 percent of its value, falling $4.36 to $2.58. In two days, the stock has fallen 75 percent.

HOODIES TAKE A HIT: Shares of two teen retailers, Abercrombie & Fitch and Aeropostale, fell sharply after they warned of weak second-quarter sales. Abercrombie sank 15 percent, losing $4.96 to $29.06. Aeropostale slid 33 percent, shedding $6.37 to $13.08.