Shares of American Apparel Inc. fell more than 18 percent on Thursday after the apparel company said same-store sales fell 6 percent last month.

The Los Angeles clothing manufacturer and retailer also announced preliminary total sales of $60.5 million, also down 6 percent from the same period a year earlier. But preliminary full year sales were up 3 percent to nearly $634 million.

Chief Executive Dov Charney noted that same-store sales had jumped 15 percent in December 2012, so there was a tougher comparison with December 2013, which was preceded by a late Thanksgiving that led to a compressed holiday shopping season.

"Although December was disappointing, and we could face a challenging environment for the remainder of the winter, our management team is energized,” Charney said in a statement. “We are excited about our prospects for spring and summer 2014 as well as for the calendar year as a whole."

Shares closed down 26 cents, or 19 percent, to $1.14 on the Nasdaq.