The incident happened on Skipton Road Esso at 3.45am today. (5 April 2019)
A man carrying a knife approached the cashier and demanded cash and cigarettes.
He left with a small amount of money and tobacco products and was last seen heading in the direction of Majestic Wine, opposite the petrol station.
He was wearing a white balaclava and thick black coat with the hood up. He had black gloves, black jeans and black trainers.
Officers attended the scene immediately and carried out a search of the area but were unable to locate the perpetrator.
Forensic tests have been carried out and police are currently investigating a number of leads, including CCTV footage from the area.
Anyone who saw anyone acting suspiciously shortly before the incident, or anything else that could help detectives with their enquiries, should contact North Yorkshire Police on 101, select option 2 and ask for Harrogate CID.
You can also contact the charity Crimestoppers anonymously on 0800 555 111.
Please quote reference number 12190060727 when sharing information.