Carfax won't give you a list of previous owners. It will tell you where the registration was paid.
Best thing is to go to DMV and talk to them. Especially, loosing the title and not knowing where the previous owners live. But if they did file a bill of sale with DMV, like everybody should, then the info should be in the system saying that they released all interest in said vehicle and who the buyer is, with his drivers lic # too! If that was done, then he should be able to go to the DMV and apply for a lost title.