If we can't get an address to either party to mail a certified letter then a private investigator must be hired to locate them. 

Establish an emergency fund and target stable long-term rentals or short-term rentals in markets you understand.House hacking or private lending can offer alternative entry points depending on your risk tolerance and hands-on involvement.

Or should I get a private mailbox in Oregon and use that?

Begin by targeting distressed properties in gentrifying neighborhoods, securing financing through hard money lenders or private investors, and focusing on cost-effective renovations.

They are also useful for private phone conversations and could be used for storage of valuables as they could be locked.I'd love to be able to broach this idea with other nationalities and cultures but it's really hard if they're not working very long hours and have hours of free time at home.  

I took a small private loan and bought my first home.

You could explore a private note sale but without hard collateral it could be difficult and would come with a discounted buy out.

We are unable to meet our financial goals.I don't usually speak ill of anybody but we decided we needed to make an exception.So be forewarned, fellow investors - there are disgusting people out there, running predatory companies with zero ethics - that will prey on investors and mistreat them in the name of "PRIVATE" lenders, right here in the United States!!

I took a small private loan and bought my first home.

Yeah I am a huge proponent of free markets and private property rights.