Razephyr

I believe Luna's been there from the very beginning, you just never see her since she's on the very last page of the album! My guess to get her though is by completing the story, Nightmare Moon being the main antagonist and all. I can't say for the Android version...as I use a ipod touch 4g, but it may be similar. I have to refresh my friends page every so often to see if another friend pops up on the list or not, they also get automatically added in there if they send a gift. It's annoying not having everyone already in there, but it's also kind of fun watching the list slowly expand.