Advice 1) Read Getting Real by 37 Signals at http://gettingreal.37signals.com/toc.php
Advice 2) Hire a decent lawyer, and attempt to recover the money you have paid to this "developer". There is a saying in hindi called "Lato keh bhoot bato sah nahi manti" meaning... Ghosts who need a kick in the ass don't agree with words. I think you owe your investors to pursue every route to get the money back. Talk to your investors. They might be able to help on the legal front. Yes, it will take swallowing your pride and admitting you f*ed up by bring this person into the deal but honesty will take you a long way with good people.
Advice 3) Decide on the right development plan from here to launch. I'm assuming you've got a business model that focuses on generating revenue not eye-balls. If not, quit now!
Your primary options seem to be a) develop yourself b) outsource to offshore c) outsource to students at nearby university.
From what you've mentioned so far, I wouldn't recommend developing it yourself. Learning the language is a good idea to know what a good job looks like.
Outsourcing to offshore is fine if you find a good team. A client of mine has had some serious problems with his India team. Proceed with caution. You need to be clear on deliverables and get constant "back-ups" of the code. This way you can tell if real work is being done... and have an early detection system of getting screwed.
There are university juniors who may be knowledgable enough to take your code and run with it. You may pay them or offer a equity share. Students usually have expenses even if they are low. So expect to cover them. Also, use all your resources in rewarding them. It's obvious that you are personable and have interesting friends. Help your developers get connected. So regardless of whether your startup succeeds or not, your people will have a strong future.
The fourth unlisted option is to find a quality company who has a reputation for getting shit done and paying them a fair amount to get your product live. This will take money. And this could come from money recovered from your ex-partner.
Advice 4) Start selling. Yes, start selling before you have your product. If you have a purchase order for $10k, your investors will probably match it. You'll need to get creative.
Most of us, both developers and entrepreneurs, have been screwed at one point... or will be at some point in the future so I feel your pain.
Just remember: "A diamond is just a hunk of coal made good under pressure." ~ Rod Weckworth
I wish you the best.