When I first read about #posh it really seemed like a very good idea to me, we just have to be constant and not stop doing it.
I'm not a very frequent Twitter user, I use more Facebook than Twitter, so I'll publish my posts on both social networks because I feel it will be more efficient. I'm not sure how hashtags work on Facebook, but I think they work just like Twitter.
It's an incredible initiative, but we'll have to work on it very well to see equally incredible
Edit: Apparently I have better results on Facebook (posts on my fb profile) :)
I'm admin of a fb group of 10k people, maybe this will help a lot :)