A MASKED robber threatened a female service station attendant with a garden tool before stealing cash overnight in Alexander Heights.
The offender entered through an unlocked door at the Mirrabooka Avenue outlet about 2.10am.
He was described as about 170cm and had his head and face hidden.
Police and the canine unit searched the area without success.
Anyone with information can contact Crime Stoppers on 1800 333 000.