The teen is accused of targeting the Enhance petrol station on Fern St at 9.30pm on April 3, while the attendant, Joe, was there alone.

Security camera footage from the store shows the masked figure threatening the attendant with a gun. He made off with cash from the till and cigarettes, fleeing on foot towards Werri Beach.

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Investigators from Lake Illawarra Police District made their arrest about 9.10am on Friday, after inquiries led them to stop a car on Burra Street at Gerringong.

The teen was arrested and charged with robbery armed with an offensive weapon. Police later searched a home at Gerringong and seized items for forensic examination.

The teen was refused bail in children's court on Saturday. He returned to court on Tuesday.

Joe, who is working part-time at the service station while studying a Masters of Business Management at UOW, said he had taken time off work in the aftermath of the hold-up.

"I was working as usual and a guy came in with a gun, with his face fully covered by some kind of scary mask," he said.

"I was a bit scared because he pointed a gun at me, I didn't know if it was a real one or not. He just took [the money] and ran away. I was a bit shocked. I took 2-3 weeks off."

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The international student said he was stunned to learn that the man accused of the hold-up was in fact a child.

"My god - it's shocking to know that. I didn't expect him to be [a child].

"When I was 15 I was playing around with my friends, not robbing stores."