How would I do that from here in the UK? What are the chances of some two-bit scam getting the full resources of the FBI focused on it even were I a US citizen?
That's why I keep asking if someone from the US has done it yet. Even so, a carefully worded email from the UK might work.
The FBI concerns itself with all crimes that cross state borders, like this one. Magnitude is irrelevant, even if it is only a few thousand dollars. If someone where to post all the evidence that has been presented in this thread to them it should be fairly easy for them to check a few records without leaving the comfort of their office. It's fairly easy to trace money as it moves around. Payment from Amazon/Kickstarter, transfer to wife's bank account, spending on resources for her new company.
Unfortunately, despite it being their job... I doubt the FBI would get involved. They are somewhat like the Supreme Court in that they have more work than they have resources, so they most definitely pick and choose where to spend those resources, often making decisions that baffle the casual observer.
The best bet would probably be the Attorney General in the state Shawn West is located in, as well as the prosecutor at the courthouse that has jurisdiction over his home address. Both are political offices and usually prosecutors and AG's have political ambitions and anything that will make them look good - especially something that will get a lot of press coverage - is something they will be on like white on rice.
It would probably also be helpful for anyone whose been ripped off to contact the police department in his home town. If one does it, they will likely consider it a civil matter. If they get dozens of people saying they were ripped off, they are more likely to investigate and/or hand it over to the county prosecutor to investigate bringing charges.
A couple of other effective methods might be to compile a "complaint" with all possible supporting documentation and then send that to his work, to the owner/President. Since, IIRC, he divulged where he worked, his actions tarnish his employer to an extent, and if he were my employee, I'd compel him to either fix the situation or find somewhere else to work.
And last but not least, buying a domain with his name in it and putting up a website that details what has happened would be perhaps the most effective thing. He's posted pictures and details of his life and his facebook page, so putting as much identifying info along with the complaint on a website that will start coming up first when someone searches for him is going to provide a TON of pressure to get the issue resolved and get the site down.