BlackFIRE made an astute observation in her comment on this post when she said that there is a certain type of man and a certain type of woman that will approach each other in public/be open to being approached in public.

For the rest of us, we meet doing some type of shared activity (like you said volunteering or it could be a hobby or school or whatever). As a young woman, I thought I would be approached simply because a man thought I was pretty, but that's apparently not the case.