You want the Xbox Games tile, that will show your avatar animating from time to time. It's listed simply as Games in the main app list. Oh and it can't be the small tile, those aren't "live" other than in some cases a counter. Need to use medium or large.
I got my avatar go to show up rather than the grey ghost by downloading the "Xbox Extras" app and I changed my avatar's clothes and saved it and now my avatar shows up on the Xbox games tile.