Many thanks for starting this thread, Eagle. I was on vacation to Venice Beach (I'm British) at the time of Max's disappearance and remember seeing the missing posters stuck up everywhere. On returning to the UK the case just always stuck with me and I have checked in on the case every few months ever since. I too have always noticed that virtually no leads have ever been published and that the case seems to be totally cold at this stage. I guess we can't begin to know how Max's loved ones feel and I'm certain not a day goes by when he isn't in their thoughts and hearts - but after so long I'm sure there must have been an element of acceptance. Whilst the optimist in me hopes that Max is alive and well somewhere, I am with you when you say the chance of that is slim to none.
So what can we rule out in terms of Max's fate?
Suicide - No suicide note, as far as we are aware nothing supporting Max wanted to take his own life and most importantly no body or trace of one. At 2am I don't feel Max was taking a boat out to the middle of the ocean, tying weights to himself and sinking to the bottom of the ocean etc. After the act he most certainly wouldn't have been able to dispose of his own remains. In a City as built up as LA and with so much time passed where development would have taken place I think the chance of him finding a secret little space somewhere to have taken his own life and that is still undiscovered is pretty remote.
Accident - Again no body or any remains have ever been found so this is highly unlikely. You could make an argument that say Max had a stash spot for something somewhere very remote, he went to it in the early hours of the morning, could his arm trapped and starved to death. Highly unlikely but I put accident above suicide in terms of liklihood purely based on a missing persons case in the UK. It is widely believed that this young RAF serviceman, whilst drunk on a night out climbed into a dumpster to sleep it off, a rubbish truck made their collection, he was crushed and dumped at a landfill which after a very short space of time becomes extremely difficult to ever find someone again. Check out
Disappearance of Corrie McKeague - Wikipedia.
Starting a new life - We have no evidence to support Max was so miserable or had so much trouble he would just skip town in the early hours of the morning and for a decade allow his family (who clearly love him very much) believe he is dead. There surely wouldnt be a missing persons case if he went into witness protection. Also I highly doubt a young man like Max would have had the financial means or connections to start a new life, identity and stay off the radar for so long.
So in my opinion that leaves foul play as the most likely cause of the disappearance here. Am I remembering wrong that there were hints that Max may have been selling marijuana? I also seem to remember reading something from Max's mother where she mentioned an associate of his said something along the lines of "nothing good" when asked if he had any guess as to what happened to Max. This was such a long time ago though I may be putting more exaggeration on this than what I read in the first place. If true though obviously you have to explore did Max tick of the wrong person(s) and met his end. Absolutely terrifying if a young man just selling a little pot would be "wasted" and body disposed of without a trace by a competitor.
I like your theory of Max going tagging and something happening to him. Good call on the Harsh link. Also whilst I know absolutely nothing about the subject, my guess would be early hours is prime tagging time. So the thinking would be he's out at this hour and bumped into the wrong person. I'm still a little hmmmm that the body could have been disposed of so well after a random encounter. Whilst given his age and small size I would say Max was an easy target to attack, but to get rid of the body so quickly surely the attacker would have had to have some prior planning in place.
Another theory I want to put on the table is that Max left to go and meet someone unknown at this time who planned to kill him. I will be blunt and controversial here now. Max could have gone to engage in sex with another man totally oblivious to what this person had planned. I don't believe any information on Max's internet history has ever been released, but this would be potentially very valuable. Picture the scene, Max is on a hook up site, he's invited to an address, he goes and at some point during the meeting he is murdered and his body disposed of. I want to stress that Max's sexuality is irrelevant, my theory is based entirely on a likely reason to visit an address in the early hours of the morning. Of course Max could have been catfished believing he was going to meet a woman, but it then becomes less likely he would have entered the address.
I personally don't feel it matters at all even if Max was a graffiti artist and potential drug dealer. He was a kid and young people make mistakes. It still fascinates me what a mystery this case is. I truly hope that answers come for the family one day.