Long time Vacant property.....how to get ahold of owner

[Kevin Stalbaum]

There is a SFH in the subdivision my in laws live that I drive by almost daily taking my daughter to grandmas. The house has been unoccupied/vacant for at least 3 years. Multiple village notices posted on the door for tall grass, repairs, etc. I looked up the status of the property tax bill and taxes are always paid before due date. Tax bill goes to the owners to a separate address (PO box in same town). I mailed a yellow hand written letter but came back undeliverable. What are next a steps people take when trying to contact owners? This house is absolutely the ugliest house in the neighborhood and is ripe for an investor. Any advice is appreciated. Thanks in advance.