The suspect entered the store at 740 Stony Point Road at about 6:15 p.m. and gave the cashier a note demanding money. He then brandished a firearm and walked the cashier to the back room of the store where he placed several items into a duffel bag, police said.
The suspect, who made off with an undisclosed amount of cash and property, was last seen fleeing on a BMX-style bicycle, according to police.
Santa Rosa police and the Sonoma County Sheriff's Department searched the area for the suspect, who remains at large.
He is described as a white man in his 20s, about 180 pounds and 6 foot 1 inch. He was wearing a hooded sweatshirt, baseball cap, sunglasses and jeans.
Anyone with information regarding the case is asked to call the Police Department's Violent Crimes Investigations at (707) 543-3590.