Facebook Forms
Taking your form offline
Once you're done with your form and you don't want to show it online anymore, one solution is to simply delete the Facebook App via the Facebook developers section. But that's not very elegant: any existing links to that page will become broken. So instead, all you need to do is change the status of the form to "offline". Once that's done, anyone visiting the form will see a custom message that you want them to see.
Here's how it works.
In the Facebook Forms module (listed on your Form Tools Modules page), click the edit icon for the Facebook form you want to take offline. There, on the first "Main" tab, change "Status" to "offline".
At this point, your form is offline. However, you probably want to customize what people see when they go to the page. To control that, go to Labels/Text tab and scroll down to the "Offline Form" section. There, you can change the title and content of the page.