This case truly is strange. If no foul play or involvement from CH himself in anything criminal, The feds, Secret Service, U.S. Marshals and Texas Rangers would NOT be involved.
Adults are very allowed to "disappear" from their lives - no matter if they are 18 or 21. And would not result in such a heavy response from the feds.
The public has been mildly interested as a whole, and the press has pretty much dropped it - so no pressure there.
CH was not a governor's son, or a son of an important ambassador, or anyone our society deems "important", not even a celebrity (sad but true).
He is not even "a blonde haired woman gone missing" and it was not on federal grounds.
If there is no "foul play" in this, the feds have a lot to answer for - putting so much effort into a then case on an adult choosing his way of life. Would they be willing to answer to that?
Now, I have trust in LE.
Therefor, there is only two things that could have happened: he met up with someone not known to his inner circle, the "plan" might have worked, or it turned into something bad (he is himself involved in something illegal or the person he is involved with is)
Or, he met up with someone he trusted, online or in person, that had very bad intentions.