There are NPCs that have Thief, because I remeber it used against me once. But you don't need to worry, because you will get your item back at the end of the battle(unless it was a disposable item that was used like a berry). You can steal NPC's Pokemon's items using those moves though.
Edit: Sorry you cannot steal an NPC's item in generation 6, only from generation 4 and below. You can only steal items off wild Pokemon.