At 9pm on Tuesday 9 November, the suspect entered a service station on Seacombe Road at Seaview Downs. He threatened an employee with a Stanley knife and demanded cash.
The employee gave him money and the man left the business on foot, heading west along Seacombe Road.
Southern District patrols, PolAir and Dog Operations Unit have attended the scene and searches are continuing.
The suspect is described as being Caucasian, short, in his mid 20s, with red hair, wearing a blue mask, a navy hoodie with an Everlast logo on it, and a dark cap or beanie.
No one was injured.
Anyone who may have witnessed the incident, or sees a man matching this description in the area is asked to call Crime Stoppers on 1800 333 000, or online at www.crimestopperssa.com.au
