How do I track down a car I owned in 1979?
Start with the person you sold it to. If that person is not available, talk to that person's relatives or friends. Then, keep it going through the same process with succeeding owners. It could very well have been junked and than compacted in a junkyard. Then, you would be out of luck.
That happened to me once. I traced the car through 2 owners and discovered it had been totally wrecked in one year since I owned it.