Connect your game to Facebook by tapping the Game Settings icon located in the upper right corner of your game screen.
Go to the Settings tab and tap the Connect with Facebook button. You can also connect your game to the Game Center/Google Play account.
Note: If you are still unable to connect, make sure you have enabled the game to use your Facebook account. You can do this by finding Facebook in your device settings and making sure it allows FarmVille 2: Tropic Escape access to Facebook.