The suspected assault happened on the eastbound 105 Freeway, west of Lakewood Boulevard, around 2:30 p.m. on Nov. 7.
Authorities said the man presented himself as a law enforcement official and signaled a woman to stop her vehicle. The suspect then inappropriately touched her during a search.
"He eventually got her out of the car, took her to the right side of his vehicle and in the guise of a search he groped her," Capt. David Moeller said.
He is described as being in his 30s, standing between 5 feet 9 inches and 5 feet 10 inches tall, between 180 and 200 lbs, with a medium build. During his stop, he was wearing a dark-colored, long-sleeved uniform style shirt with tan pants.
On his shirt, there were shoulder patches, a silver star type of badge and a silver nametag. The suspect also had a black police-type of utility belt with a gun and Taser.
"He didn't identify himself as a law enforcement official. He just appeared as one to the victim," Moeller said.
The vehicle he was in was described as a black four-door sedan, possibly a Ford Crown Victoria, with red and blue emergency lights mounted inside the windshield and rearview mirror. He also had a spotlight on the left side of the vehicle and his front and rear windows were tinted.
Anyone with more information was urged to call the CHP at (323) 982-4900, attention investigator DaSilva case #2017-04333-550.