If you don't have a new address from him, mail it with delivery confirmation to the rental address (his last know address).If he still owes you money after that, then I recently found this collection agency, which I've never used, but in your shoes I would try them out. 

Then again hawaii houses are built differently and we dont wear shoes in the house so I guess softer stomping ;).  

5 years ago I was in your same shoes I analyzed several markets and landed on Memphis TN. 

I am sure they live there, not staying over, because I saw his clothing & shoes in the closet in the room, with a few boxes of size 4 diapers that can only be for his son but not the tenant's youngest daughter who is going to be 3 yo soon.

Try to pretend you are in their shoes, and what it would take to make you happy or cooperate.

Put yourself in their shoes. 

When you buy the place, you buy the contract, too, and just step right into the shoes of the previous owner of the contract.  

I don't need to wait until I'm scraping it off my shoes to avoid it and it sounds like you don't either.

We need health to create wealth.Good pair of safety glassesVoltage detectorGlovesDust maskSteel toe shoes, saved my toes a couple of timesEar plugsHard hat for attic work

To me, one is an act of kindness, the other would be funding what equates to a gambling addiction.I'm glad I'm not in your shoes.