So I've played Teemo for several games, and here is what I think of him
He needs a minor rework.
You only pick Teemo for 2 reasons: to troll, or to have map pressure. He's not that effective at 100-0 anyone, he certainly can't tank, and he doesn't have great dps unless he gets ahead. The change suggested below is to resolve this.
W: Scout's Code: Passive: If an enemy champion appears in Teemo's true vision, or is revealed by the vision provided by his traps within 2500 units of Teemo, Teemo gains 35 / 40 / 45 / 50 / 55% bonus movement speed when moving AWAY from that champion for 4 seconds. This can only proc on each champion once every 25 / 23 / 21 / 19 / 17 seconds.
Active: Teemo instantly gains 25 / 34 / 43 / 52 / 61% bonus movement speed for 3 seconds. While this effect is applying, if Teemo runs into a bush, he instantly gains his passive stealth.