Teen retailer Aeropostale Inc said on Thursday its second-quarter net profit rose 75 percent, helped by lower costs.

But the U.S. company's forecast for third-quarter earnings was below Wall Street analysts' average estimate, and its stock fell 0.7 percent in extended trading.

Quarterly net profit was $14.7 million, or 19 cents per share, compared with $8.4 million, or 10 cents per share, a year earlier. Wall Street analysts, on average, had been expecting earnings of 19 cents per share, according to Reuters Estimates.

Net sales increased 13.3 percent to $311.2 million. Analysts were expecting sales of $326.15 million, according to Reuters Estimates.

Sales at stores open at least a year, a key retail measure known as same-store sales, fell 4.1 percent during the quarter.

During the quarter we were able to generate strong increases in our gross margin, Chief Executive Julian Geiger said in a statement.

For the third quarter, Aeropostale expects earnings of 43 cents to 45 cents per share. Analysts were expecting earnings of 49 cents a share, according to Reuters Estimates.

Aeropostale shares fell to $22.95 in after-hours trade after closing at $23.12 on the New York Stock Exchange.