Restarting the app solves many issues (crashing, freezing, etc.):
For iOS:
-Tap Home button twice.
-Locate your game in the app display by swiping left and right.
-Swipe up on the game's image to close the app.
-Tap Home button and then restart the game by tapping it's icon.

For Android:
-Go to Settings -> Applications -> Manage Applications.
-Select your game and then tap Force-Stop to close it.
-Re-open the game to restart the app.

If the issues continue, uninstall the game, then download the game again and re-install it.

If none of these steps work then fill out the trusty form to the left describing your issue/bug and our support team will work to resolve it ASAP!