I am not in LE but I think it is safe to conclude that the types of evidence of foul play they look for include weapons, drugs, known threats to the missing person, signs of a struggle, blood stains, and in the case of cars, things like broken glass, an accident, unusual stains, car being found off the road, etc.
None of these things happened here. The guy literally walked away from his known life. Not a crime in any jurisdiction so no justification for LE to expend limited public resources on an adult runaway.
It's obvious the car was not a crime scene; the idea, in this case, would be that **the crime took place elsewhere** (and likely far from SCA, with the car merely being "dropped" there).
A runaway could DRIVE away, not park.
A runaway wouldn't continue to use his cellphone, AFTER parking in a secret place to avoid detection.
A runaway would at least take their computer with them, to communicate.
A runaway would need clothes, and at least a small travel bag.
And most of all, a purposeful runaway would need to have created an entire new identity and financials, to carry it off.
Classifying this case as "a walkaway" makes it easier for the police.
I HOPE it's a walkaway, but it's been too long -- and I really don't see Steven as someone who could abandon his friends and family for this long.