Who to mail yellow postcard to?

[Jason Le]

I started my investing business and started to do bandit signs, but I also want to do yellow letters or post card. I have yet to know the response of either and would like to do both as my marketing campaign but I want to know who do I mail them to? Do I just mail to anyone or a certain group(absentee owner or vacant/inherit houses)? Where do I find people that are in need or is interested in selling their houses?