The entire river heading out to the ocean would be mostly unsearchable until it gets warmer. Divers can only stay down so long in the cold, and it is too full of roots and trees for any kind of underwater crawling robot. Any area of forest, while officially searchable, would take a very long time (I think of Dylan Redwine's case and all of Middle Mountain...fluke to find his bones in a water runoff culvert). Add to that the weather, so people have to stop and start-takes a lot longer. At look at that terrain around the river. That is not easy searching.
I am not familiar with LE saying they needed new info to go on in order to have places to search, but I miss some articles.