Ask HN: How to find a co-founder?

I find people everyday that are interested in working with me, but most of them just lack enthusiasm to like, run a company(which is a difficult task). How did you find your co-founder?

I find that sometimes I get people amazed by what I'm developing, I get asked by them to participate. I let them in and after some weeks I stop seeing results from that person(that sucks). How to deal with that?

Is there a website to find motivated and skilled people to find it? :)