Advertising broadly for a co-founder is like running an ad that says: BRIDE NEEDED FOR IMMEDIATE BABY PRODUCTION. You might get somebody eventually, but I doubt it will be the caliber of person you want.

I found my cofounder after 3 months of energetically working my personal network. I corresponded with maybe 200 people and met at least 25 in person. If I was going to be spending the next 5-10 years working with somebody, I wanted to be happy with my choice. And I sure am!