How can I add this face to the game?

You can either follow the steps outlined in this thread to manually add them yourself, or you can wait for the forthcoming update pack (which should be no more than a couple of days in coming out) which would add it and all other images released since the previous pack.

P.S. The forum moves so quickly that if you just post on a player's timeline, it is quite unlikely that it is spotted, unless somebody happens to be around when it is posted. I would suggest that you either post in the main forum (maybe in the megapack home thread), or tag me or another staff member so that we can get a notification and are aware of it 👍