Here's what I'm starting to think....
I was really confused about the whole asking for help from the President but canceling a local event, so in trying to make sense out of it, I have kind of a theory. Maybe the family has an idea of what happened, and there are specific steps that they want taken, but they don't want to share those with the public for whatever reason. Maybe, as some have suggested, an influential family is involved, and they feel they need something more than SAR and local fundraisers? Maybe they feel anymore local attention drawn to the case will only make things worse somehow, like maybe they are fearful of the perp or believe that if Holly is still alive she might be harmed? Or maybe - and I hate to go this route, but we have to explore every possibility - maybe Holly was involved with something that they don't want coming out in the public, and while they are grateful for all of the help they do trust local LE and know that there are certain things that need to happen for the case to be solved, so maybe they don't want to see people waste their time and resources or get anymore involved, but they also don't feel like letting us all in on everything. Maybe LE does know that Holly is not in the area and that SAR efforts would be useless, but they can't tell us that for whatever reason.
These are all just ideas, because I can't come up with any other possible explanation. Like others have said, with any other missing persons case where the family is not involved they always say they would do ANYTHING they have to do bring their family member home, and I know that's how I would feel if that ever happened to me. At the same time, they've now got people all over the country who never knew Holly who are interested in their personal business, posting publicly about her, collecting photos of her, organizing events, etc. It's got to be kind of uncomfortable for families, on some level. Of course, no matter what the truth is, they should just want her found, even if something embarrassing would come out (not suggesting it would, just saying it's a possibility), but I think it might be more complicated than that.
I think the family knows a lot more than they are telling the public, but I don't necessarily think they were the ones who harmed Holly. I think they have a strong sense of what this is all related to, though, and maybe when all is said and done (assuming it ever comes to that point) we'll be able to see why they didn't want the public to know everything or why it wouldn't do any good if they did.
Again, I don't necessarily believe any of these things, but they're just theories.