The victim, a 25-year-old man from Brigg, was driving a white Ford Transit van on Tuesday morning.
He was delivering parcels containing items of furniture in Mill Crescent, Scotter. It is not yet known the exact contents of the parcels.
At around 9.35am he was approached by a man who pushed him to the ground.
The offender then took the van keys, got in the vehicle and drove away.
The van driver was not injured.
It is not known which direction the van travelled once it left Mill Crescent.
The van is marked with Lincs Van Hire written on the front, back and sides. The registration plate is YP61 0CN.
Police believe the offender may have emerged from a silver estate car, but this is yet to be confirmed.
He is described as being of skinny build and around 5ft 8ins - 5ft 9ins tall.
He was wearing a black hooded top and dark blue tracksuit bottoms.
Anyone who may have witnesses any part of this incident, or who might have seen the van or the silver estate car before or after the offence, is asked to call the police.
Likewise, if anyone knows the current whereabouts of the van and its contents.
Contact Det Const Kev Kay of Gainsborough CID.
You can call the non-emergency number 101 and quote incident number 81 of Tuesday 4th September 2012.
Alternatively, you can call the Crimestoppers charity anonymously on 0800 555111.