Time for a Private Investigator?

[Ori Skloot]

 Did some driving for dollars near one of my properties in Oakland and found a boarded up property. I looked up the property and found the owner's mailing address. Sent some letters and then went over to the owners house to knock on the door. Discovered that house was abandoned as well.   I went back to the first house and spoke with the neighbors - apparently there was a murder at the house (details were scarce) and the owner hasnt been seen for a year.  Ah, the plot thickens.  So I do a skip trace (TLO) on the owner. All the phone numbers are disconnected and there are no relatives.  No other listed addresses.  Slam right into the proverbial wall. 

Anyone got any tricks up their sleeve for a next step?  I thought about posting a for-sale sign in the front lawn but it feels a little sketchy to do that in this neighborhood.

Has anyone in the Bay Area ever tried hiring a private investigator to find someone who is trying to stay off the grid?