This is quite possibly the most unsettling thing in I’ve seen in Homestuck.
It is incredibly powerful, and it invokes a feeling of emptiness and panic. In all 6,000 pages of Homestuck there has never been a time where you have truly lost track of someone. They are never lost, because somehow the narrator always manages to find them again.
The line “John Egbert has gone missing” is the realization that you are no longer in control.