Q: Personal Hotspot has disappeared on iOS 6.1

This may helps you.

iOS: Troubleshooting Personal Hotspot

http://support.apple.com/kb/TS2756

iOS: Understanding Personal Hotspot

http://support.apple.com/kb/HT4517

Just came back from Genius Bar with the same problem. Tech told me this is a known bug, and "Reset all settings" would solve it, but "Network reset" would not. An so, it did. Immediately. I asked why apple hadn't posted it on the technical page linked above. He shrugged his shoulders. DO a general reset. It won't wipe your data, but will reset your ringers and lock settings etc to factory.

Setting >> General >> Cellular >> Cellular Data Network >> Reset Setting

Restart (hold on/off button >> slide to power off)

My Hotspot turned off and disappeared from Settings Screen. I went to Settings>General>Cellular>Personal Hotspot and toggled the "off" to "on" and back to "off" and the Hotspot reappeared in Setting Window.

That was certainly less stressful than doing a "Network Reset" and worth a try first (it was also easier than schlepping the phone back to store to have them figure it out as Verizon suggested)!

Only follow my instruction go to the settings ,General,software update ,you will see the icon appeared then update your device to the latest iOS  version it 100 percent works I had the same problem ,it was solved only by doing this simple things