I was reading the coroners reports for Riverside County and looking at other crimes in the area. What makes this disappearance stand out from other crime in that region is that most of the time when someone is killed, it's obvious. And the gang related deaths follow a similar MO. Someone pretty much gets shot where they stand, no one attempts to hide the murder.
There have been some missing young women cases that didn't turn out well, where the bodies were hidden, but there was nothing like this case where two, or even one young person almost seems to evaporate into air, and their vehicle is left so neatly behind-showing no obvious signs of foul play.
It's unusual. And I don't know what this means, but I do believe that a crime occurred. So maybe we are looking for an unusual perp/s.
There was a story on Dateline that involved a family from Fallbrook, CA. The story of the family had some similarities and unfortunately had a sad ending. And the were no signs of foul play and some clues pointed to them wanting to disappear (certain internet searches). Its a great episode.
https://en.wikipedia.org/wiki/McStay_family_murder