Tracking down an owner of a property, How can I do this

[Adrian Valdez]

Hello forum, 

I have been actively sending out yellow letters in an area near me these properties are boarded up and I want them. Recently one of my yellow letters came back in the mail because forwarding ended for this person. Now I want to ask how would you suggest I go and track this person. I originally got their address through the tax records of the property so I am kind of at a loss where to go from here. 

Thank you for any info 

Adrian