Finding a co-founder is almost like finding The One, but as Anna from Frozen learnt, you don't marry someone you just met. You need a relationship, a history together or even some mutual friends.
Like in dating, prince(s) charming doesn't have to answer a "list of criteria" in order to be a goof match, but he or she must have complementary sides in his or her skills (and preferably personality as well) or there is a small chance to have a synergy in you two building a company together.
Now that you know all this, start by looking at your friends, and at your friends friends. Can any of them be the right fit? If not, there are a lot of Meetups and other events that declare that they are co-founders "matching events". look for them and start dating. It is not idle but can be successful.
another way, that in my opinion is more risky, is post am ad on LinkedIn and in the right groups on Facebook, you will find great people there, but you will have to work harder on building your relationship, as personal relationship between the partners is not only very important, it's vital.
Good luck