I think the number of people who won't use meetup exceeds the people who won't use facebook at this point. I despise facebook but it's a necessary evil. Meetup is just a terribly clunky site I hope I never need to log into ever again. I go to some meetups that happen to be on meetup, but find the times elsewhere, or they're a weekly meetup so I already know the time. They may have dominated the space, but if you use meetup, some will just ignore the meetup group.
Another way to go is the old fashioned route of posting physical paper fliers on telephone poles, or bulletin boards in cafes, universities, and libraries. It's local, absolutely free, and usually there's so much junk there that something serious and actually interesting would stand out.