The squeaky wheel gets the oil.
If I were a family member I would be raising all sorts of hell in every police station that has been involved in ANY piece of this situation. Stand in the middle of the station and scream:
"I'm not leaving until someone gives me some *bleeping* answers! I am not going to go away, I'm going to go to the national news and tell them you told me finding a missing person "isn't your job"! I'm not going to take no for an answer - and don't tell me it's not your job because IT IS YOUR JOB!"
And then, because I'm kinda crazy like this, I'd throw in "If you want to tell me it's not your job, that's fine, then I'll make it mine...but don't you DARE step in when I find out information and serve up justice without you" - and then I'd start walking out.
GUARANTEE YOU someone will stop you. You will get SOMONE'S attention. You aren't making a direct threat to anyone in particular - you are making a statement that won't allow them to ignore the severity of the situation. Demand someone do something. Do NOT take "we can't do that" or "this isn't our jurisdiction" BS answers - find out who's jurisdiction it is, and go to them...keep being loud and annoying until one of these jackholes gets so annoyed they either tell you what they know (and are working on) or they take some action.
No way in hell would I be tolerating the "not me" games they are playing. I'd be so damn annoying to every single person on that force it would drive them insane...