Thieves drove off in two cars when they broke into a car dealers in Billingshurst.
Police say the thieves forced open a key cabinet at the premises on the A272 in Coneyhurst Road and used the keys to steal a Fiat 500 and a Seat Leon.
Officers say it is believed the cars - both white - were driven in convoy north into Surrey.
The break-in happened overnight between Tuesday October 15 and Wednesday October 16.
A police spokesman said: “Anyone who saw anything suspicious in the locality or who noticed the cars on the road is asked to contact Sussex Police online (https://www.police.uk/contact/af/contact-us/) or by phoning 101, quoting serial 257 of 16/10. Officers are particularly interested in securing any CCTV or dashcam footage that may help with their enquiries.
“Alternatively, information can be passed anonymously to the independent charity Crimestoppers, telephone 0800 555 111.”