Pick someone that you know (not necessarily a friend), but take a few precautions.<p>First, this person may completely change their character under pressure or a feeling of impending doom, just as you need them the most. You can work with someone in the same low stress job for years and you'd still be in for a surprise when the going gets rough.<p>Second, you need to walk a very fine line between selling them on your idea on one hand and making sure your future prospects and goals are aligned. Selling someone a dream is easy, but it's just not enough for coping with the ongoing brutal wear that's startup work.<p>Third, make sure this person complements your skills with as small of an overlap as possible.<p>Fourth, assign responsibilities from day one, and aim for a vesting period for stock ownership (for all founders!) so if he ditches, you won't find yourself with a defunct company.<p>So to sum it, it's not so much about where to find a cofounder, as much as it is managing the process and expectations.
I agree with @alain94040. The best co-founder are your former classmates, co-workers, and the other people you have already worked with and know. Look for really smart people who are around you that possesses a skill that you lack. i.e. If you're technical, try to find somebody who is business oriented.<p>I would also hit up Meetups, Users Groups, and maybe Alumni mixers. Chances are you might run into an old co-worker/class mate that shares similar interests.
Hope this helps: <a href="http://www.slideshare.net/alain94040/co-founder-issues" rel="nofollow">http://www.slideshare.net/alain94040/co-founder-issues</a><p>The best co-founders are people you already worked with. Go back in time, even for ex co-workers you think wouldn't be interested, meet the ones you deeply respect and start meeting with them for coffee.<p>Maybe they'll be interested, or at least they can recommend someone else they trust who could be. Repeat.