The attack happened on Aug. 8 in the area of Malden and Wilshire avenues.
Investigators say the suspect sexually assaulted the woman, 19, after cornering her on the stairs at an apartment complex.
The victim said she saw the suspect loitering in the apartment complex approximately 30 minutes before the attack. During the attack, the victim screamed and struck the suspect with her cellphone, which caused him to release his grip. That's when the victim ran to safety.
She described the suspect as a Hispanic man with dark skin, about 30-49 years old, about 5 feet 6 inches tall and weighing about 200 pounds. He has black hair, brown eyes and appeared clean shaven. He was last seen wearing a red baseball-style cap with an unknown logo on the front.
If you recognize the suspect or have information on the assault, you're urged to call Fullerton police at (714) 738-6762.