ATLANTIC CITY — Police were looking for an unidentified juvenile who dropped a gun in a school gym Thursday night, causing it to fire. According to Atlantic City police, officers responded to Dr. Martin Luther King Jr. Complex at about 9 p.m. Thursday after a commotion caused by a crowd running out of the gym. Police said a handgun was found on the floor, and no injuries were reported. Detectives from the Street Crimes Unit were investigating and attempting to identify the juvenile, police said. Anyone with information was asked to call the department’s Criminal Investigations Section.