If you are looking for a co-founder and not a contractor for-hire, then it is important to source one from within your closest contacts. Ideally, choose a good friend.

Not only does the co-founder need to share your vision, they need to tolerate/accept/embrace you personally, and you them. You will go through tough times together.

If you prefer to call the shots and carry the burden of founding, then don't get a co-founder: just retain and pay a contractor, as many others have said here. It's good advice.

The illusion of a co-founder is debilitating for startups. Every founder must be putting in devoted work. It's a gunny-sack race they're in, not a baton-race, not a solo-marathon/sprint.

So find someone close to you who appreciates you personally, otherwise, hire an expert.