The 4×4 vehicle, which is the older model of the Discovery and has tinted rear windows, was taken from outside a workshop at Pickhill at about 7pm on Friday 17 January 2014.
It had been left for a short time while the owner was inside the building.
A suspicious black Land Rover Defender was seen nearby at the time of the theft.
Officers are urging people to come forward as soon as possible with any sightings of the stolen green Land Rover Discovery or the black Land Rover Defender.
They are also keen to hear about any suspicious individuals who were possibly seen in the area on Friday or recently, such as door to door sellers.
If you can assist the investigation please contact North Yorkshire Police on 101, select option 2, and ask for Northallerton CID. Or email CIDNorthallerton@northyorkshire.pnn.police.uk
Information can also be passed anonymously to Crimestoppers on 0800 555 111.
Please quote reference number 1214008982 when reporting details about this incident.