If he's an NPC, he doesn't live in the town, and he could disappear at any time. The best thing to do is find him with Master Controller ASAP, and move him into a house. You don't actually have to find him to do that. You can just click on any house, select MC, then Add Sim and find him in the menu. You can add him to your own household instead, then you would be able to control him. He would lose his job at whatever venue it is, if you do that, but then you could get him a job with set hours, making it easier for your sim to spend time with him.