At about 5:45 p.m., the victim descended from a BART train at the South San Francisco station, police said.
She was walking southbound on the Centennial Way trail when an unknown male approached her and asked for her name.
When the woman refused to speak with the male suspect, he grabbed her by her arm, according to police.
The woman was able to break free from the suspect's grasp. She began running southbound on the trail. The suspect chased after her for several feet until she passed another pedestrian, at which point the suspect his pursuit, police said.
The suspect has been described as possibly Hispanic or Asian, about 30 years old and between 5 feet 7 inches and 5 feet 9 inches tall, with a medium build.
He was described as clean shaven, and was wearing a white, long-sleeved hooded sweatshirt with the hood up and dark-colored pants or blue jeans at the time of the assault, police said.
Anyone with information is asked to contact police at (650) 877-8900.
South San Francisco police are encouraging citizens to avoid walking alone, especially in secluded areas.