Runaway investigations, how do they work?

Just out of curiosity what is the police department’s procedure on runaways? I mean the minute a cop hears "she/he ran away" do they just stop listening. It no longer becomes important? Because this inexperience child left on their own. it’s to their own demise what happens? I’m not trying to trash the cops at all. I’m really just curious. I feel the that PD in our city who is investigating my BFF’s step daughters case just don’t really care, they are giving us lame *** answers. Don’t get me wrong when I first found out this angry 16-year-old girl decided to bone out on her own. I thought ok, she’s doing what teenagers do. She’ll be back in a couple days when she needs a shower or gets hungry. No biggie. Till I find out she’s with a offender THEN! I freak out THEN! I want the cops on this like white on rice. But they could careless. Why is that? After a week of being gone she finally made the news. ONLY! Because this dirt bag she’s with has a warrant for not registering as a of