I FOUND TETO, you need to use surf in the 7th gym town near the bridge and go up to the lighthouse. Then talk to the bunny and Sans. After, go to route 3 with the boat guy and go to a volcano area. There's a cave in said area and in it is Teto.
Oh wait, I also had the butterfly on me, so that may have played a roll (but I don't think it did for Miku, so I doubt it)