Hey everyone - there is an easy way to restart and you don't have to create a new Facebook account. 
All you have to do is the following. 
1. Delete the game from your device. 
2. Using a computer, open a web browser and log into Facebook. 
3. Once logged in, on the left hand side of the screen, you will see a section called "Apps". In this section, you will see an icon labeled "Games". Click on it. 
4. You will now be in a screen that shows you a bunch of games that you can play. At the top of the screen, you'll see a few links titled "Find Games", "Your Games", and "Activity". Click on the link titled "Your Games". 
5. In this screen, you should see an icon for Simcity Buildit. Below the icon, you'll see a button that is greyed out that says "On Mobile". Right next to that button will be another button with a little gear on it. Click that button. 
6. In the pop up window that just opened, there is a link at the bottom of the screen that says "Remove App". Click that link. 
7. Another window will pop up asking you if you are sure you want to remove Simcity BuildIt. Click "Remove". 
Congrats, your game is no longer synced with your Facebook account. 
Now, redownload the game to your device. Upon starting the game, you will start over from square one (tutorial). Upon completion of the tutorial, design your new city the way you would like. 
At any point, you can click the "settings" button in the game (which is the little green screwdriver and wrench icon), and tap "Login with Facebook". Doing this will sync your new city with your current Facebook account. 
You can do the above each time you want to start the game over and have access to your "new" city on any device you play the game on. Note - you HAVE to sync your city with your Facebook account in order to be able to access it from any device. 
Hope this helps!