I'd also like to answer "blogs".
I run Standalone Sysadmin, which sort of caters to small infrastructure sysadmins. I've got around a thousand subscribers and of those, a couple of dozen people who come back again and again to comment and interact with each other. It's great to see.
In addition, there is a social network setup specifically for sysadmins, called creatively, The Sysadmin Network. It's devoted to helping sysadmins communicate to each other.
Join user groups, join a professional association, like LOPSA, SAGE, and go to (or start) local chapters of the above.
I've seen time and time again that there are always more people interested in joining a group than there are people interested in starting a group. Once the momentum is going, people jump on the bandwagon like there's no tomorrow.
To advertise your usergroup (or whatever), put ads in papers, local website, local businesses, whatever you've got. Trust me, the people are out there, they just have to be found.
Sometimes all it takes to get a group going is to find that one old grizzled sysop that used to run the community BBS. The old BBS people probably got together back in the day, but now that the net is here and the BBSes have died, they don't have a reason. Give them one.