The thing that strikes me about this case is that there really aren't that many scenarios in which both (little) Deorr is outside the search are, and all POI's are completely honest.
All I can think of that fits is either Deorr wandered off beyond the search area (possible), or he was attacked by an animal (unlikely, but possible).
In my (unqualified) opinion, what is most likely is that the search and rescue wasn't good enough, and Deorr is within ~2miles or so of the campground, or one or more of the POI's aren't being completely honest.
Animal attack is possible, of course at this point with so little information nothing can be ruled out, but IMO it seems highly improbable. The animal would have to have taken Deorr, and left little to no evidence behind (eg, blood, Deorr's cowboy/camo boots, no evidence of a scuffle, broken branches/twigs, etc), or perhaps it did but the search teams didn't find it. Not to mention the lack of scent picked up by the dogs. Although that doesn't mean there wasn't one.
Deorr could have fallen into the creek or reservoir, but again it seems pretty unlikely that he wouldn't have been found by now. Wouldn't he have surfaced by now? How far could the rocky creek have taken him? It's level must be even lower than it was when he went missing.
Deorr could have wandered beyond the search area, it's not impossible. But there appears to be no evidence for it. No boots have been found, no scent was picked up the dogs, searchers found nothing to indicate (eg, prints, crushed grass, broken twigs, etc) that this happened.
So if we move into the realm of what I consider more likely, we are left with Deorr being somewhere within the search area, and I certainly don't discount this. These type of things appear to happen a lot. People, especially small people, are hide to find, and as nature takes it's course it only gets more difficult. Certainly a possibility. Of course the other scenario that is also a possibility - again, nothing should be discounted, is that there is some sort of deception going on (the sheriff appeared to rule out stranger involvement, so obviously that leaves the 4 POI's). In my opinion this possibility was bolstered once the FBI became involved.
Personally I am very frustrated with this case, as I'm sure we all are. I hate to say it but this (IMO) has all the makings of a cold case. I mean it's pretty much cold right now. I hope Deorr is at peace wherever he is.