By now you should have figured that all of the steps actually go back to the participation thing. People can't show if they don't know.
If your event is spontaneous in nature, you can:
- Create an anonymous email account (it's best that your event not have an easily identifiable leader) and send to 50 random people in your address book. Ask them to send it along to another 20 people.
- Post to bulletin boards like www.Craigslist.org. You can post to the Events board, or target a specific demographic by posting to specific discussion forums (kink, vegan, divorce, etc.).
- you can also use sites such as www.xflashmobs.com to sms message your mob to cell phones, but this will require that you establish a contact list, which isn't very spontaneous.
If your event is more elaborate:
- Post to local event calendars and discussion groups. The following are pretty good bets: