S&P SmallCap 600 in Focus: HOTT REGN

The index--which tracks stocks with a market capitalization between $300 million and $2 billion--gained 7.03 points, or 1.8 percent, to 399.76.

Small-cap companies make up about 3 percent of the total U.S. securities market, but are often cited as good investments due to their low valuations and potential to grow into big-cap stocks.

Shares of Hot Topic surged 95 cents, or 18 percent, to $6.22 after the retailer said sales at stores open at least a year fell 0.2 percent. Analysts polled by Thomson Financial expected sales to decline 2.4 percent.

Tronox Inc. climbed 39 cents, or 10.7 percent, to $4.05. The maker of titanium dioxide pigment said Thursday it was raising its prices in North America, Latin America and the Asia-Pacific region.

Cabot Oil & Gas Corp. jumped $6.18, or 10.5 percent, to $62.25 after the Houston-based company said completed a deal to buy 25,000 acres of oil-producing properties in Eastern Texas for $602.8 million. The company said the fields have proved reserves of 176 billion cubic feet equivalent.

The declining stocks were led by Regeneron Pharmaceuticals, which plunged $3.69 to $15.39. Analysts at both Credit Suisse and Morgan Stanley downgraded shares of the biopharmaceutical company Thursday.

Martek Biosciences Corp. lost $2.16, or 5.8 percent, to $35.36 after the dietary supplement company said its second-quarter profit rose 89 percent but still came in below Wall Street estimates.

Aircraft components maker Triumph Group Inc. lost $2.88, or 5 percent, to $55.07.