I have personally given up on finding a co-founder randomly through these match sites. Everyone has their own agenda and you cannot start a company with strangers. I know some people succeed with these platforms but for me, it just hasn't worked. May be I haven't put in enough effort. But the idea of starting a company with a stranger or someone you just met seems crazy.
Look into your own network first. I know it is not always easy if most of your network is not entrepreneurial but you never know. I hired someone in my team out of a corporate job who used to be my co-worker 10 years ago. He is not co-founder but an excellent team member for our small company.
If not your network, I truly believe that it will be accidental. It could be someone you may work with and realize that they are lot more than just a co-worker/team member. I truly believe it has to be accidental.
True co-founders have to know each other well especially how they behave when shit hits the fan and shit WILL hit the fan if you are working on a serious company.