ROTTERDAM — Police are investigating an armed robbery reported Tuesday night at the Dollar Tree store at 70 W. Campbell Road in BJ’s Plaza. Police received a call at 8:45 p.m. that the store was robbed by a man who displayed a handgun. The suspect is described as a white male wearing cut-off jeans, a long-sleeved gray thermal shirt, a navy blue baseball cap and a white bandana over his face, police said. He is of average build. After taking cash from the register, he fled on foot toward Putnam Road. Responding offi cers searched the area with the assistance of Schenectady police and their K-9 unit. Also on the scene were the state police and the Schenectady County Sheriff’s Department. Police were unable to locate the thief. Anyone with information regarding the suspect was asked to call the Rotterdam Police Detective Division at 355-7397.