When I reveal Teemo and they react with Gust, do I still get Teemo's effect or no?

Yes, you still get Teemo's effect, though its impact will be limited.

According to the RiftJudge FAQs (3559, 3204), when you reveal a unit like Teemo Strategist from Hidden, its "When I defend" ability triggers and is placed on the chain. If your opponent reacts by playing Gust to return Teemo to your hand, the following occurs:

1. The Chain Resolves (LIFO): Gust resolves first, returning Teemo to your hand.
2. Teemo's Ability Resolves: Even though Teemo is no longer on the battlefield, the triggered ability remains on the chain and resolves. You will still reveal the top 5 cards of your main deck and recycle them.
3. Damage Fails: Because Teemo is no longer "here" (at the battlefield location), the damage portion of his ability cannot find a valid reference to deal damage, so it deals 0 damage.

In summary: You still get to perform the reveal-and-recycle portion of the ability, but the damage portion will fizzle because the source of the effect is no longer present on the battlefield.