Was it a normal delivery truck? Like a UPS truck or anything like that that had specific colors? or even white. It's not uncommon for them to hit people and try to get away, because they get fired for it, unless it wasn't their fault.
Also, if it was some sort of box-lorry or something like that, not a lot of people own them, and it was probably rented, look for a truck rental company nearby, and look around their stock for a truck with damage where it hit you or ask them if anyone rented the specific truck you saw, and you can get their name.
If you can't find the truck driver, you'll have to say a hit and run, but you don't have any info otherwise. If you have a picture of the truck on your phone, though it's low res, you may be able to get the plate number off it, if you took a picture of the back of it, upload it here, and I have some software that may be able to get the plate number even if it's a bad picture, and you can go from there.
Also, if it was some sort of box-lorry or something like that, not a lot of people own them, and it was probably rented, look for a truck rental company nearby, and look around their stock for a truck with damage where it hit you or ask them if anyone rented the specific truck you saw, and you can get their name.
If you can't find the truck driver, you'll have to say a hit and run, but you don't have any info otherwise. If you have a picture of the truck on your phone, though it's low res, you may be able to get the plate number off it, if you took a picture of the back of it, upload it here, and I have some software that may be able to get the plate number even if it's a bad picture, and you can go from there.