The biggest challenge I've seen so far to find a co-founder is that you need good reasons to spend time with the person before you screw anything because you actually dont "match" with the person. The process is awkward socially.

Therefore, meeting someone for the reason of wanting to co-found a company is probably not the best way to find a cofounder. Going back to university or going to hackatons works probably better.

Though, maybe what would work as an app for example would be to collaborate on fake projects because that way you sure you wont screw anything.