direct mail

[Kong L.]

I have a question I need help with. I went driving around looking for vacant house and found two within the same block. I sent them each a yellow letter that I am interested in buying their property. I haven't heard from one of the house but the other house, the mail returned stating on the envelope "return to sender vacant unable to forward" right below the address.

What way can I find out of where the owner(s) moved to? (I went into the county public record and it is still showing the same address for the property and mailing address, which it's the address I used.)

thanks in advance