The incident occurred outside a public restroom on the popular wharf shortly after 8 p.m.
The victim was not injured in the assault, according to police.
The suspect was seen in the company of another man and both men ran away from the area before officers arrived. Officers searched the wharf and surrounding beach area but did not locate the men, police said.
The suspect was described as a white man, between 25 and 45 years old, around 5 feet 9 inches or 6 feet tall, with short brown hair. He was wearing a white tank top shirt, according to police.
The suspect's friend was described as a white man in the same age range and around the same height as the suspect. He has a heavier build than the suspect and was wearing a black t-shirt with a swirl pattern on the front.
Anyone with information is urged to call 911, Santa Cruz police at (831) 420-5820, or the anonymous tip line at (831) 420-5995.