BOSTON -- Arlington police are searching for a man who scared some high school students by flashing them Thursday night.

The Arlington High School students, females practicing field hockey, said they heard some one whistling and looked around.

The saw a man, exposing his body and touching himself.

They said he then took off on a nearby bike path. He was described as a balding white man, with a large forehead, about 6 feet tall.

Police believe the same person did the same thing to a group of young people several days before near the Mystic River.

Officers asked people to be alert on fields and in parks in the area and to report any suspicious activity to police.