James Currier and the NFX team run an accelerator that is basically an expert level boot-camp for teams specifically focused on Networks, Marketplaces (and now, other verticals).
The team was way ahead of the inherent value of 'marketplace' & 'network' focused teams, and I would highly recommend them as a resource to any young to mid-stage team focused on marketplaces/networks/etc. (Note - they are industry agnostic, focus specific). Very founder friendly, and good folks.
Also, I'm happy to answer questions for any founders looking for help developing a marketplace/network.
(Full Disclosure - our team was in the first batch of the program.)