There are a few of you on here that are hitting this right on the head, not because it is my personal theory, but if we actually ignore each other's theories and listen to the audio and look at the video, it very clear these girls (in the beginning) felt semi-comfortable with this man and his voice almost shows a familiarity with the the girls, meaning he was familiar with them as if they have ment before or very possibly knew them.
It was pointed out in an earlier post that "it felt like they were directing these pleas towards a certain person". They are, they know who this person is, just not where. That's why I believe this man had past ties with the community in some way. I have a strong feeling that this man had previous knowledge of this family via a family friend or a relative ect. I strongly believe atleast one of the girls had mentioned a previous encounter with this man to an adult possibly even a parent, but was more than likely brushed off because this man was "kinda" known to them. Yes that sounds absolutely ridiculous, but if he was known as a shirt tail relative to one of the locals or just a seemingly nice guy people have bumped into on occasion in town, the girl saying she seen him in the trails probably wouldn't of raised any concerns with the parents. A huge statement was made in a post here, that the Father could be the positive identifier of the man..Bingo!. I could see the the shame and embarrassment in his face aswel as the Police Officer, they brushed shoulders with him on the trail system.
It is no fault of the Father, he was in "find mode" and everything else just didn't matter a that time.