[ After the way Hera had wiped their memories and then proceeded to make both Percy and Jason her champions in the fight against Gaea which also included launching seven demigods and their satyr guardian to the ancient lands, yeah, Camp Half-Blood would have had a huge fit. They already had to deal with other demigods disappearing into the nearby forest so they don't need more missing individuals.

Those left at Camp also don't know a whole lot that's been going on with Apollo's quest since they left either so something could have happened with that too. ]

If they are then they're pretty powerful for no one to notice his disappearance. Personally, I suspect it has something to do with this place.

[ Somehow he doubts that the Triumvirate has the power to make a demigod just vanish and no one else notices. Especially one of the Seven who's pretty much a legend by either Camp standards now. ]

Need us for what, exactly?