No need to trouble them with having to fill out a tax return postcard, lets just establish a NST...

Many times the neighbors know what happened.Just tell them you are looking to buy houses in the area so that you can clean them up, and get them occupied, and you saw this one looks vacant, and could use some TLC.Most of the time, they will not give you the persons contact info, but if you give them your card, they may reach out to the owner.2) Send a letter/postcard to the house, using a first class stamp and mark "Return Service Requested" under your return address.

Of course there's the postcarding method of trying to buy properties but has anyone taken that a step further and tried approaching people in person?

I tend to DIY everything the first time and afterwards determine I never want to DIY again. This time its direct marketing to out of state absentee owners. Designing my own cards, having them printed from Ebay. Then I...

Two things come to mind:Send a postcard with return address correction requested, The US Post Office will find the forwarding address for youWww.findtheseller.comI've heard good things about that website

I was thinking about mailing a post card to former cash buyers?

That being said, it is possible that this lot is ready to go, simply needing infrastructure buildouts - assuming that the thousands of postcards sent to the owner over the years have gone unread, and that he has no telephone service, etc.

Then I have 500 postcards that need to mailed. 

The small win that I achieved was being able to successfully trace an owner of a property from a post card that was sent back to me as "return to sender".

Postcard marketing is expensive!