I've been wondering the same myself and wouldn't say that this forum is the best place to start - not because there aren't good developers here but because they're unlikely to work with or advise you, unless you've already got a really good idea and a working project to plug into. You sound like you're starting from scratch, so you might want to first read up on basic computer security and blockchain dev't. Not to understand the tech but to familiarise yourself with the languages and tech that the developer would need to have. That helps you narrow down your search.
Be warned that a lot of the freelance devs out there are only entry level people - they're probably good enough if you just want a simple project (think all those ERC20 tokens flying around) but if you're building from the ground up... you may have to headhunt. The very best devs in my opinion are already tied up... and I'd say the world's top ones are all with Bitcoin.
But they give you clues about what a top blockchain dev is, how they're different from the general coder/programming population. They're passionate (I hate the word, but in this context it fits entirely) and very ideological.
Linkedin is a good start, sign up if you haven't and advertise for some developers
I suggest advertise your specific needs and criteria to the project
Best way to look would be - Full stack development / blockchain, you would find a lot of programmers
And this is a really good starting place to headhunt, especially if you sign up with an employer account. A pretty good way to cast your net is to attach a small test (you'd be surprised how many freelance coders fail basic aptitude tests that don't actually require programming knowledge).
But I think if you really want good blockchain devs, you go to where they live and spend a lot of time to seek them out. Here. Blockgeeks. Blockchain conferences (meet real devs there).
