Driving for dollars - a lot of return mail, any ideas?

[John Hyatt]

I have been driving around my area of expertise in Phoenix, Arizona and have mailed around 20 postcards to the tax mailing address of the owner of the property listed on the Maricopa County Assessors website. About half of them got returned as wrong address. Is this normal? I hear a lot of investors say they get deals driving for dollars. Is there a better way to get in touch with the owner? I usually mail to the houses that look vacant or are in need of repairs. Thank you in advance!!