The incident happened on May 23 at a Walgreens on the 300 block of North Sepulveda Boulevard.
Police said a female driver noticed a man in an SUV following her. When she parked at the Walgreens, the man parked next to the woman's car and started touching himself inappropriately.
The female victim ran into the Walgreens, and the man followed her, according to police.
"She tried to hide in between the aisles," said Lt. Raymond Garcia of the El Segundo Police Department.
Surveillance video shows the man wandering around the store, apparently looking for the victim. The woman eventually left the store and went to police.
Police said another victim has come forward. She told police she was stalked by a man driving the same SUV on the 105 Freeway.
The suspect was described a 35- to 45-year-old black man with medium build, 5 feet 9 inches to 5 feet 11 inches tall. He was clean shaven and bald or had very short hair. He was wearing a white T-shirt and white pants at the time of the incident.
The vehicle the suspect was driving was described as a metallic blue 2005 to 2010 Lexus RX330 or RX350. It had damage on the left rear corner.
Residents in the area say they are concerned that there may be a predator on the loose.
"I think everybody has to be aware of their surroundings," said Kay Steele of El Segundo.
Anyone with information is urged to call El Segundo police at (310) 524-2216.