A Tower Local Controller reported an aircraft on short final advised they were going around due to a vehicle on the runway.

Narrative

Aircraft X was an IFR flight that I had already cleared to land for RWY XX. I also had an Aircraft Y in the pattern to RWY XY who was cleared #2 for a touch and go. When Aircraft X was very short final; he declared he was going around due to a vehicle on the runway. At that time; I was looking up at the Aircraft Y to make sure the sequence worked and to ensure separation for a second; eastbound Aircraft Y. I had never spoken to a vehicle to allow them access to any runways; so I rescanned and still didn't see the vehicle. I stood up; stepped to the side and that was when I saw a pickup truck on RWY XX. I told Aircraft X; Roger; go around. I asked on frequency; Who is on the runway; but no one answered. I said again; There's an Ops vehicle on the runway. Who is on the runway? Ops X answered saying it was Truck Y; and he thinks something blew out of his truck. I informed him that doesn't mean the vehicle can enter the runway. I never was able to get in contact with the offending vehicle; but I did observe him exiting RWY XX at Taxiway 1. The vehicle was no factor for my touch and go on RWY XY. I confirmed with Ops X that the vehicle would not be reentering the runway. Aircraft X was instructed to enter right traffic for RWY XX and landed without incident.As this was happening; another controller called Airport Operations via the Ops line and was informed it was a contractor in the vehicle and they would be sending someone out to take care of it. There are large structural poles impeding the line of site to multiple parts of both runways. Unfortunately; the only solution would be a new Tower with fewer line of sight obstructions.