There are online resources to help you in interviewing coders but they're probably not going to help you find the best people for your team/product.
A founder better know at least someone they trust who codes for getting feedback on their idea. No product just gets made without critical input from engineers and tech. If your startup didn't take this into consideration you're more than likely going to have bigger problems than hiring quality coders.
Whoever that trust board is that helps in forming the company and the ideas behind the venture should also be used to hire your first tech lead. This person should be on top of their game and know how to own the tech side of the project, find and hire other coders, and make informed decisions about the vector of the project that they can explain to the stakeholders. But the beginning hire is done by someone who can vet and be trusted.
Lastly, hire on a short-term contract basis at first so you're not committed long term if it isn't a good fit.