One thing that I find ineffective with men's responses in online dating: They seem to want immediate reaction/gratification. Such as in if they email you and want to meet you, they want to meet you NOW!
The problem is, most women, including myself, want to meet someone, but we can't always rearrange our lives to meet you today or tomorrow. I don't know how many times someone has emailed me, wanting to get together right away, and when I say I can't get together for a few days or a week, I don't hear from them again.
What that tells me is that you are not that interested to begin with, and then why should I bother? If you can't even wait a week to meet someone you say you are interested in?