Twitch doesn't carry with stealth, he carries by playing like a carry. Just because you have stealth doesn't mean you have to be a secret agent and then pop out in the middle of their team like a pink elephant.
He's just always absurdly squishy. The rest of your team needs to be unignorable, intimidating, or have a LOT of catch and peels in addition to you keeping the maximum distance that you can from the fight. This isn't any different from what any other ADC ideally wants, but Twitch is especially susceptible to mobility champions.
Teemo's somewhat safer because he has a mini ghost with movefast. Good shroom coverage is arguably stronger map control than playing mobile ward with Twitch.