Learn how to response to people in a correct way, when they ask for someone by this english conversation.
Don't just say No. You will make them feel worse. If possible, give them some clue or idea how to find.
Example 1
You : Where's John?
Friend : Isn't he in the office?
You : I didn't see him there. If you see him please tell him to drop me a line. Thank you.
Example 2
You : Have you seen John today?
Friend : No. I havn't.
You : If you see him could you tell him to call Peter?
Friend : Sure.
Example 3
You : Is John around?
Friend : He might be in the pantry.
You : Can you tell him that the boss wants to see him as soon as poosible?