Finding owners that are "unfindable"

[Terry Royce]

I have two properties that I have been working on for a long time. They would be great projects.
However, I CANT find the owners contact info.
Both properties have the owner's mailing address listed in public record as being at that premesis and clearly they do not live there anymore. I've done reverse searches on the names etc and am at a dead end. I've left business cards at the premesis.

What are my options from here?