Keep a detailed record of your attempts to reach them and their responses (or lack thereof).

All 3 of the "owners of record" on the tax records were deceased.The seller was the son of one of the deceased. 

You can try to check the county recorder's office and see if that comes up with anything.

However, be aware that the IRS closely scrutinizes REPS claims, so ensure meticulous record-keeping and documentation of hours to substantiate your status.

Do you search criminal records for them?

I have had multiple units in the past that dragged my down a lot more than propelled me forward, and I was happy to dump those.

In most municipalities you will have to pay transfer taxes equal to the assessed value even if transferred for a nominal amount plus deed prep and recording fees.

A good private money lender should be transparent about terms and fees, have a solid track record and experience in real estate, and demonstrate flexibility in tailoring loan options to meet your needs.

I would simply record things when they actually happen FOR YOU.

Private money lenders primarily lend money based on trust and your track record.