I've been sending message to new users that are in our meetup area, inviting them to join our meetup. I also offer to answer any OSM questions they have. Since Jan 2015 I've sent 106 messages. From the new users, I've received responses from 10 new mappers. That's a 9% response rate.
Not sure why the response rate is so low. A couple of possibilities come to mind. First, I don't ask for a response. While I do invite them to join our Meetup Group, it is impossible to find a match between OSM user_id and Meetup nickname. Some could have responded by joining the meetup group. The other possibility is that I need a better welcome message. There is a third possibility but for now I'm not going there.
Work in progresssss