So. You're telling me that Stiles goes missing. Scott hits up alla his homeboys to go find him. And out of all of them, Mr. Fucking Badass Mysterious Broody Derek Hale is the FIRST one to hunt down where Stiles was last seen. Derek recognized Stiles' scent from memory- he didn't need to go by Stiles' house to pick up a stronger scent or a fresh scent. He got that shit burned into his brain, unconsciously or not he knew how to track down Stiles.
Now you could interpret this as Derek just knowing how important Stiles is to Scott, and everybody is out here trying to protect the new True Alpha and Stiles, wolf or nah is a member of the pack, and blah blah blah.
Or you can accept that Derek messed around and fell one too many times into the awkward little arms of the adorable, dorky, and yet Brave Stiles Stalinski and to his deepest embarassment fell in love with Scotts weirdo best friend.