The game offers 25 coins as an incentive to log into Facebook in the game, but these are only credited once per Facebook account. If you log into the same Facebook account again, even on a new device, the coins won't be credited.
If you haven't logged in before and still have not gotten your coins for logging in, please contact our Support Team by submitting a support ticket in the game; you can do this by tapping the "gear" icon on the map screen, and then "support," or you can open an online support ticket here.