I see this question asked a lot on the Main Real Estate Forum. Here are some of my ideas on how to locate the owner of an abandoned property.
Go to www.ancestry.com, click on "search records," then click on the right on "social security death record." This will allow you to check if the owner has passed away. Write down the birth and death days and location.
Check at www.ancestry.com in the general search and see what other things they come up for that name. (If it's John Smith, you might as well forget it.)
Search at http://www.searchbug.com by name.
If you have found a death record of the owner, go to the vital records office and buy the person's death certificate ($10 to $20, depending on your state). It usually lists an informant, which may be relative or friend, who might still be at the same address. You can also go to www.vitachek.com and order it over the Internet, if it's a different state.
Go to www.ussearch.com and search for the owner's name for free on the main page. They will only give you cities and ages of people with the same name, but not exact addresses. You can then search www.searchbug.com, if there's a listing in that city.
If you can't pinpoint it in the free search, pay for a search through www.ussearch.com or www.docusearch.com. The more details you have the better.
Check with www.google.com and see if the owner is mentioned somewhere.
Go to probate court and check if probate has been filed. If it's an unusual name, check files of other deceased people with the last name. They might be family and other relatives, who might know the whereabouts of the home owner.
Search through the marriage records in probate court and get the spouse's name or find other relatives' names, if it's an uncommon name.
Check if the taxes are being paid, and if they are, check with the tax commissioner's office to see if they have the address of the person paying.
Do a small title search at the courthouse and check out all documents in relation to this property or the owner. Maybe the house was bought from another relative.
Check out any liens and lis pendens. The owner and anybody with a claim on the property is usually mentioned in the documents.
See if the owner owns other properties and check out those documents for clues.
If it's an unusual name, check property records for others with the last name. They might be related.
Ask the postman and neighbors if they know more details. Ask neighbors if the owner had any children. The children may still have friends in the neighborhood. If the owner had a child, find out the age and check with the school for that neighborhood, would the school forward a letter to the child, if he or she is still in the same district.
Explain what it's about, so that it doesn't look suspicious that you're asking about someone else's child. Explain that you may be able to help the child's family out of a tough situation. Just some thoughts on how to possibly find owners of abandoned properties.