Q: personal hotspot in iphone 4 is missing

The personal hotspot depends on your carrier if it allows you to have one. if not then its not gonna show up in your settings. just confirm by calling customer care or checking their website. if they do allow it then check cellular setting or by restoring or reseting the phone.
hope it helped

if you go to Settings> General> Cellular and then Hotspot you will be able to turn the feature on to operation.

Thx kennethfromnaxxar,  this answer saved me as I was unable to restore my missing personal hotspot (it had moved to General>Network and was not accessible). I could not restore it even with Factory Reset. So pay attention guys this may be the answer for you if you have a disfunctional personal hotspot.

Hi, the Personal Hotspot option disappeared from my Settings control panel AS I WAS ACTUALLY USING IT. Your mileage may vary, but what eventually worked for me was to open Settings --> General --> Mobile Data --> Personal Hotspot: switching it on and off again returned the tab to the top-level Settings menu. Weird.  Good advice here: http://ipod.about.com/od/iphonetroubleshooting/qt/Fix-Disappearing-Personal-Hots pot-In-Ios-5.htm and here: http://www.hongkiat.com/blog/iphone-personal-hotspot-missing-fixes/

Go to settings, go to general, tap on cellular, scroll down , see personal hotspot , tap it , turn on

The "Network" button isn't under General either?

And Cellular doesn't exist under General on my Iphone either...

You really think someone who posted 4 years ago is going to answer you? And they are referring to a much older version of iOS, Cellular is its own section under Settings in iOS 8.3.

Or simply turn the phone OFF (truly off, all the way -> press the button in for a couple of seconds until the slider shows on the screen, slide to turn off). Then turn the phone ON. It will restart with all settings available, including HotSpot.

Not a bug. If you don't use it, it takes itself off to not confuse you.