you seem to have some imbalance in completing the stories. misty is at a quite progressed part of the story. but the panty thief is quite early in the story. also, you will never find the 3rd panty, it is kinda inside her. spoiler alert^
i think he is referring to the pair you cant find (selenas).. just search her room, then report back to my cat. you'll find out why you cant find them later (she has special clothes) Spoiler alert ^ again