In this recent post to her blog Elizabeth Naramore looks at something some development (and really any type) of community struggles with - growing their number of active, engaged members.
From my experience, one key to a successful online community is the sort of magic that happens between community members that keeps it vibrant and growing. You can't force that kind of magic, and you can't clone it. It just happens.
She points out just a few of the resources you and your groups can use to help get others involved including wikis, mailing lists, IRC channels (I hear Freenode is nice) and twitter. She also gives specific examples of PHP-related community resources she's involved in like the PHPBuilder.com forums, her local PHP user group and the PHPWomen group.
What makes a community tick? [...] I'm no psychologist, but I can offer up a few words of advice for those struggling to grow their community or find that magic. Lay all your cards out on the table and see which ones gather momentum. [...] Let the group grow naturally and remember the complexity of the group dynamics is what dictates how the group will gel, not the leader.