Witnesses saw the attacker run in the direction of a nearby subdivision, police said. He was described to officers as a tall, thin man in his late teens to early 20s. He was wearing a black and white shirt with dark pants.
Police are asking area residents to be on the lookout for someone matching this description in the area of the park, which is also home to the local Boys & Girls Club.
Anyone with information is asked to call 911 or to contact Monroe police Detective Chris Cannon at 770-266-5183 or 678-357-1939.