Plenty allow retail investors, e.g. Lending Club and Prosper. That said, I can't really advise participating as a retail investor since institutional investors

Plenty allow retail investors, e.g. Lending Club and Prosper. That said, I can't really advise participating as a retail investor since institutional investors employ technology (that you have no access to) in order to instantly scoop up loans that pass their models (which you also have no access to).