The main thing to do when looking for a co-founder is to stop looking for a co-founder.

Seriously.

Think about "what skills am I lacking to complete this business on my own."

Then, look for local groups that can help you to get that, whether it be a "boot camp" for coding, Some marketing seminars, something.

Your next step is to actually go out and do that thing.
While doing it, talk to people. Make friends.

Eventually (not right away), you will find someone you really click with, and you will talk to them about your idea, and they will be so fired up they will join you.