The incident occurred on Tuesday while the girls were running along the 15200 block of La Serna Drive near Dittmar Drive around 4 p.m., police said.
The girls had just finished their circuit training and were running back to school. As they ran by the suspect, he reached out and touched them inappropriately, investigators said.
Police described the suspect as a Hispanic male between 17 and 23 years old with an average weight and height. He was last seen carrying a black backpack and wearing a dark-colored shirt and jeans and a black and white bandana on his head.
If you have any relevant information about this case, you're urged to contact Detective Dineen at (562) 567-9283 or the Whittier Police Department's crime tip line at (562) 567-9299.