At about 8:50 p.m., three males in their mid- to late teens approached a man sitting in a parked car in the 1500 block of Sunnyvale Avenue.
The victim told police he rolled down his car window when the suspects knocked on it, and that one of them then pointed a shotgun at him and demanded money.
One suspect punched him in the face and another took money from the victim's pocket, police said. The three then fled south on Sunnyvale Avenue.
Police on Wednesday released images from video surveillance that they believe show the three suspects.
One is described as a short, thin black male with close-cropped hair. He was seen wearing a dark hoodie with designs on the front.
A second suspect is described as black and about 5 feet 10 inches tall with a thin build. He was seen wearing dark jeans and a dark hoodie over a white T-shirt.
The third is also described as a thin black male with close-cropped hair and thin facial features. He was wearing dark jeans and a dark jacket over a gray hoodie.
Officers responding to the robbery searched the area but did not locate the suspects.
Anyone with information about the crime is asked to contact Walnut Creek police at (925) 943-5844.