It's Hotch/Reid but there's a definite Peter Pan flair to the case. Garcia finds the names of missing girls in one of Kevin's shirts and it leads the team to finding more and more hints about the killer. One of the shirts was a reference to Alice In Chains and the last message was 'Find Wendy'.
Also, Reid was kind of...upset? at the idea of drug addicts being considered less than people. I'm pretty sure the fanfic was also posted on dreamwidth.
Any help would be awesome!
FOUND! http://cm-casefiles.dreamwidth.org/1507.html