Surveillance video shows the suspect skateboarding to the door of a Chevron gas station around 7 p.m. Monday.
The suspect walks in with his skateboard and points a semi-automatic handgun at the store clerk, demanding money from the cash register.
"It's very dangerous," said Seal Beach Police Sgt. Steve Bowles. "Anytime there's a handgun or a threat of violence we take it as a dangerous action."
The suspect tells the cashier to put an undisclosed amount of cash in a bag and leaves on his skateboard.
"We don't know if he used that as a quick exit from the area, was able to get to a car parked in a different location," said Bowles.
Police said before the robbery the suspect was seen standing outside a blue vehicle, possibly a Ford Focus.
Police describe the suspect between 19 to 25 years old, 160 to 170 pounds. He was wearing a hat and coat, and his skateboard is green in color with bold markings on the bottom.
"Based on the video we hope someone can identify the suspect," said Bowles.
Anyone with information about the suspect should call Seal Beach police at 562-799-4100.