Use a crowdfunding MVP when you are ready to pitch your product to the world. It doesn't have to be 100% there but it should be well researched and have a strong story and plan for moving forward.

Crowdfunding MVPs give a clear signal of whether your problem and solution are in line with what people will pay for. If your campaign succeeds you have a group of committed investors that you may be able to engage in research and testing and whom you will need to keep updated as your process unfolds.

Kickstarter and Indiegogo. For more information about starting a campaign have a look at The Art of the Kickstart for ideas, case studies and information.