I have a co-worker who's family has a lot of rentals, he was suggesting a piggyback loan while another who used to be a realtor was telling me about Fannie Mae bringing back 0 down grant loans.

I would rent to him and not bother with a co-signer since you already approved the other tenant.

There are only a handful of reasons you can get a second FHA loan:You’re relocating due to a new job opportunity.Your new home is more than 100 miles from your current FHA-financed home.You need a bigger home to provide for a growing family.You’re getting a divorce and your spouse is staying in the current home.You were a co-borrower for someone else's FHA loan and want to buy your own home.You're not using FHA loans to build an investment portfolio.You're buying a HUD real-estate owned (REO) property.

I was thinking of getting a Co-borrower but I would rather not have one.

It was also a friend of a co worker.  

We've had more traction advertising as a co-host company for STR and gaining people who already have STR or are buying one.

Do you know the technical differences between a Co-host and a PM company?

And you call the seller and they let it fail over to voicemail or just ring off the hook...And that's just a co-incidence.I doubt getting your money will happen on a friendly basis.As @Greg M. said, go to the Police and ask them for help.In person with the Desk Sargent is probably your best bet.If the local District Attorney will take the case they should file an investigation.If not you will probably get double talk about not enforcing civil laws and they do enforce civil laws.If that happens, Lawyer up if you think that makes sense and go after the solution.But you say you have no written rights to the rent, so was this an oral contract?

I need a co-signer.

I was thinking of getting a Co-borrower but I would rather not have one.