Best way to find a car with the VIN

[carnut4life]

I'm sure this has been discussed here before but I'm looking for opinions on the best way to track down a car with the VIN. I know there are people out there that have access to this info that occasionally go out on a limb for fellow enthusiast, which is great, but I'm figuring I need to go the PI route for the best chance to track the car down and contact the owner about purchasing the car. Is there anyone out there that has done this before that can recommend a reputable company that offers this service? Not sure if it matters but the car in question is a 1981 Z28 with a 17 digit VIN. Thank you, Chad