The guy that runs a pickup skate that I go to now and again built up his following by word of mouth, email, email, email, and now uses an evite every monday morning(for a friday skate) inwhich everyone rsvp's to. As well as using Facebook to keep everyone in tune and in touch.
Your best bet is to get your core guys that you already know, the people they know, then go from there. Use message boards, social media, whatever to get the word out.
You don't pay, you don't play. None of these- "I'll get you next week", that just causes a trickle down effect of other people doing it.. See if you can get guys to commit by paying for the first skate, and maybe a one time fee of paying for a week or two out, if they enjoyed it, that way you are covered on a week you may be short guys/money.
First anf formost though, get a solid group of guys, that are for the most part commited to playing each week. As I said, word of mouth, and social media will take you pretty far.