Call in "intuition" but, I don't believe that there's any hope of finding this poor girl alive as I don't believe that she ran away.
For some reason, I get the image of a gray bearded man...someone who hadn't shaven for a couple of days, someone Sierra knew from around the area, perhaps even a neighbor??? From what i can see, it seems that he's an older man....50's to 60's perhaps, teeth not so well taken care of, squarish face. Perhaps, someone who knew she'd be coming out of the house at that particular time because of her usual pattern so, it leads me to feel that perhaps, this man lives along the path that she took to the bus or, perhaps, close by so as not to seem "suspicious" at being on her street at that time in the morning???
To me, it feels as though she may have been coming out, it raining and never got past the end of her driveway before he offered her a drive to school rather than taking the bus that day. Kind enough sounding and because she may have been familiar with this man, she likely wouldn't have had much hesitation in taking that ride. It could be he said he was heading in that direction for some reason so, it just seemed "natural" to her to take up that offer???
Given that she had tweeted that morning before she left, it could be that she had pulled out her cell phone in the vehicle to tweet again and he took it from her hands, throwing it out the window before she could tweet again???
For some reason, I feel as though she looked up at that point and realized that they weren't going the route she would have expected to get to the school. That may be when she got panicky and clutched onto her bag or perhaps, opened it??? He may not have known what was inside so asked her to toss it out the window???
I don't feel that the used condoms were part of this case for some reason...nor, the handcuffs. But, I could be very wrong on that.
I get a feeling that her body is in behind an open field but, WAY back...into brush with a drop behind it....kind of like a ravine, covered in brush. She is not buried or under water...just well hidden behind trees and brush that no one really goes into.
I also get a shirt that looks like it's a button up, cotton style shirt....at times, it seems like a light denim others, it looks like a checkered appearance with reddish color, woven in with blue. I get differing versions of it...perhaps, a change of clothing afterwards???
I don't know the area at all and haven't looked at the maps to get any idea of where this spot is that I see her remains....just that it's off of a cut/open field....way back behind that.
And for some reason, I get an image of a "food mart" (whether that's the name or not)...white plastered building, off on its own. This may have been something that was passed by on the way to where she is????
All of this is intuitive and only my own opinion. It certainly doesn't make me right about any of my personal opinion and I'm praying for a miracle still for this young girl.