[Theseus doesn't argue with Hiccup on that, partly because he doesn't want to. In this instance, he wants to be wrong and believe that the mist won't change Newt to the point where he'd hurt innocents. It's not within a zouwu's nature, at least, but he's also not discounting how strong the mist may be.

He really wants it to be gone soon.]

Newt's not in any state to answer calls either. [...Not that Newt is good about answering them in the first place. Theseus plans on bugging him more about that later on.]

If you know a general direction, we can start there. Better than wandering aimlessly. [He nods at Hiccup.] Listen, I want you to find him, I know you're up for it.