Stuck on level 18

Jennifer13

Hi. I'm new to the forum. I'm stuck on level 18. I have to get the serum location for Raider before he becomes a zombie.... I have been in very building for three days looking for him and can't find him. Also the map isn't giving me a clue to where he is as its does with most tasks. I really need someone's help to tell me where he is otherwise I'm going to quit the game, but I enjoy playing it so really don't want to.
Any help is much appreciated
Thanks guys.