I am close to 50/50 stranger vs. friends or acquaintances.
LE seems to be considering both, since they are looking for this truck which would seem to match the story of JR, timewise; yet as far as we know, he and the others are still POI's.
I'd be surprised, however, if it turns out (assuming we ever know) that Lauren's crazy night had nothing to do with her disappearance, other than placing her in the wrong place at 4:30AM.
I am not sure as to how much that truck matches JR's timeline. LS supposedly left his apartment at about 4:30 am. And then he watched her for some time (according to btwon's calculation less than 10 minutes) but didn't see anything happen to her. The truck was last seen on camera at 4:24 am. Of course I realize JR's timeline is approximate, but they do have the exact time of the phone call made to DR supposedly by LS at 4:15 am (or so was claimed by a lawyer). So presumably based on JR's story, at 4:15 am she was still at his apartment, and she probably wouldn't have left immediately after making that phone call, if he says she left at about 4:30 am. How long would it take the truck to drive from where it was on camera to where LS was last seen by JR?