This morning I couldn't find my iPhone 5 anywhere and when I checked "Find my iPhone" it wasn't showing up, just "Not Online". I swore I charged it yesterday. If stolen, can the theif disable the "Find my Phone" app?
Yes. The phone can be restored, thereby erasing your settings and disabling Find My iPhone. (Find My iPhone is really designed to help you locate a lost device, not a stolen one.)
Retrieving data ...