A man holding a knife entered Worthing Watersports in Alinora Crescent at around 2.20pm on Monday (April, 17), a police spokesperson said.
He demanded till money from the two owners sat behind the shop counter, according to the spokesperson.
One of the victims handed over cash amounting to approximately £50, confirmed the spokesperson.
The thief then left the store and rode away on a black BMX style bike in the direction of Nutley Crescent.
Police describe the suspect as a white man, of skinny build, 5ft 9ins and in his late teens or early twenties.
He had dark brown straight hair which was collar length and spoke with a local accent, police said, and was wearing a long sleeved royal blue zip-up jacket, black jogging bottoms and white trainers.
Anyone who was in the area at the time and saw anyone acting suspiciously or matching this description is asked to report online via https://sussex.police.uk/contact-us/response-to-appeal/ or call Sussex Police on 101 quoting serial 640 of 17/04.
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