The amount of your loan is at a level where it may be cost prohibitive to hire someone to pursue payment. It is also very difficult to collect from an individual, I am not suggesting that you just forget about the loan. I would check into filing your own lawsuit. I am a Florida lawyer, but I am willing to bet that there is a "small claims court" locally in your county where you could file an action yourself. You will need to have your check and emails ready so that you can prove the loan was made. There will be a filing fee, and many times the county clerk will assist you in filling out the paper work. You will also need to have your lawsuit served on your former friend. In Florida - the process is much shorter in small claims court and you can really get someone's attention by having them served. Good luck.
Because your suit involves a "small claim", hiring a lawyer may cost close to half of your debt amount. So consider that before hiring one because if you lose, your $9,000 loss could become $15,000. Verbal, non-written contracts are difficult to enforce without the other side making certain concessions in court.
You probably cannot recover attorneys fees in this case. Therefore, it would probably be better to go to small claims court. The limit in small claims court is $7,500. You would "lose" $1,500 of your loan, but that is less than the attorneys fees would be.
I think you could sue him for the first payment and then sue him for the second payment. That may get you around the $1,500 loss. But, I have not researched that issue lately.
If you decide to go to small claims court, email firstname.lastname@example.org for my free how to book on small claims court.