The woman was walking along the Arroyo Road bike path near South L Street at around 2:15 p.m. when the suspect approached her, police said.
The two started a conversation, and the man introduced himself as "Gabe." He extended his hand for a handshake, and when the woman took it, the man pulled her close to him and grabbed an intimate part of her body, police said.
The woman yelled, and "Gabe" let go. The woman backed away from him and the suspect walked away.
Police said the man was described as a Hispanic man, around 19 years old, about 5 feet 6 inches tall and 140 pounds.
To be safe, police recommend that people jog in pairs and remain vigilant of their surroundings on jogging trails.
Anyone with information about this incident has been asked to call Livermore police at (925) 371-4900.