To dream of seeing a thief, denotes to your energy, period of time and concepts that you are giving to others. Probably the dream tries to tell you to be more focused on yourself, instead of the others. If you became a thief in a dream, then such dream shows your fear of losing what belongs to you. Maybe you feel you did not earn what already belongs to you, therefore there is a feeling of taking other peoples ownerships.
Read more about dreaming of Thief in other dream meanings interpretations.