A man armed with a knife robbed a mobile shop in the Galliagh area of the city on Saturday night.
The incident happened around 8.30pm when a man wearing a blue hooded top and armed with knife entered the mobile shop at Brookdale Crescent.
He made off with a sum of cash.
Police investigating the incident are keen to speak to anyone with information about what happened, particularly a man who spoke to the shop owner shortly after the robbery took place.
Anyone with information about any of these incidents is asked to contact police on 0845 600 8000 or via independent charity Crimestoppers on 0800 555 111.