Wow, there are a lot of search hits for the name Cory Weiss, but most are either a rabbi (who would be too old), high school athletes (who would be too young), or female (who would be too, ummm...female).
In a people search engine, I did find a reference to a Cory Edison Weiss who would be the right age; listed addresses were mostly in the midwest (primarily Indiana), but also included San Francisco, as if he'd moved there when he finished college, maybe. Parents seem to be Donelle (sometimes misspelled Donelee) Bokich Weiss and Richard Weiss, who seem to still live in the Hammond, IN area. (Note: I have no idea if this is the Cory Weiss who is missing, especially since the ages are often way off in these people search engines. Just speculating here because of the San Francisco address...but "Cory Weiss" seems to be a fairly common name, and San Fran is a pretty big city, so there could certainly be several Cory Weisses associated with it.) One searching difficulty is that the California real estate guy appears to be the same age and is also a Cory E (Evan) Weiss.
I feel like the missing Cory Weiss probably wasn't a San Francisco native. IF (and this is a big IF) his family lived a fair distance away, they may not have known about or had access to resources to publicize his disappearance in a large city they weren't familiar with. I also wonder if, as someone speculated above, this might be a suicide, so the family reported him as missing since there was no body found to know for certain what happened, but they haven't publicized it more because they kind of know in their heart that he's not out there alive somewhere. Although if that were the case, you'd think one of the missing person sites would say something like, "He was reportedly distraught" or something like that.
PS: MM, I am also a fiery redhead.
ETA: Ignore anyplace I've typed "Cody" instead of "Cory"--I've been writing a lot about someone named Cody the past couple of weeks, and my fingers keep automatically typing a "d" instead of an "r." I think I've changed all the typos above, but if I've missed one, it's just my mistake, not a speculation that he's hiding under the name Cody or anything--