You make an offer to the owner. It's that simple.
Real estate investors do that. They'll contact owners of houses--often houses that appear abandoned or at least in not-good condition--and express an interest in buying it.
In your case, a Realtor would be helpful. He/she can track down who owns the property and where they live. (You could do the same; they'll use the tax records, which are public information.) Then you put together an offer and present it to the owner. Not a big deal.
Hope that helps.