Shares of the company, which said it would close the stores this year and in 2016, fell as much as 13 percent on Thursday. Dunkin’ estimated a growth of 1.1 percent in comparable sales at its U.S. Dunkin’ Donuts stores in the quarter ended September compared with a 2 percent rise a year earlier. The company said the stores being closed accounted for 0.1 percent of its U.S. sales.