Was there a hint that this was tied to social media?
At the very beginning when the girls first went missing, the case wasn't exactly off to a great start; it seems like it took several hours to get some sea legs beneath it. But, the girls obviously used SM, and LE has had access to their accounts, etc. I would think LE would be working on those avenues more at this time, rather than hammering on this picture if they think it was rooted in online activity?
From what I have learned about this area, it appears this area was a recreational area that commonly had younger people around. If you're a predator, and you have a place with a good possibility of teens hanging out, without it being a high traffic area -- well, there's really not much to lose to taking a walk if you're a monster with something like that in mind. He wouldn't have to wait around if he didn't want to. Just cruise onto the next possible location. There also exists the possibility that he saw them, and went back to whatever he has for a home base to get a weapon and his plan together.
Also, this was a built in day to the school calendar. There are so many ways a person would know that.
I am so willing and likely to be wrong about everything and anything. It could be random as much as targeted.
it is a good thing that I can't be more predicative ; I don't think like these monsters. My brain only goes so far before it jumps "off the tracks"
PS - If I didn't "read" your thoughts properly, let me know. High volume day for posts, and I am legally blind...my eyes get wonky after a while.