The armed robber entered the Caridean Street store about 7.50pm.
He selected an item before approaching the counter and wielding the knife at a staff member.
The offender demanded cash, but left empty-handed.
He was thought to be aged 18 to 20 and between 170cm and 175cm tall.
PerthNow Digital Edition.
Your local paper, whenever you want it.Get in front of tomorrow's news for FREE
Journalism for the curious Australian across politics, business, culture and opinion.
READ NOW
He had a skinny build and was wearing a grey hoodie.
Anyone with information can call Crime Stoppers on 1800 333 000.