The men entered the convenience store, located in the 1200 block of Boulevard Way, at about 2:15 a.m. and robbed it. One man was armed with a gun and the others with pepper spray, Lee said.
The sheriff's office, with help from Walnut Creek police and the California Highway Patrol, searched the area with dogs and a helicopter, but didn't find the suspects.
The clerk was not hurt in the robbery, Lee said.
There was also an attempted robbery at the same store on June 21 and detectives were still trying to determine whether the same people could be responsible for both incidents.
They were looking to see if there was surveillance video of the robbery.