Has the phone ever been recovered? If not, does anyone know what kind of data the police could recover from its activity in absence of the physical phone itself? For instance, his movements that evening (and whether they correlate with where he was seen on CCTV), and what calls or messages he received/sent and who they were from/to?
I'm also wondering whether the police have interviewed his friends at all. The strength of feeling on facebook whenever search parties are organised suggests he has plenty of friends who would like to be able to help. So you'd think it would be possible for police to build up a picture of who was at the party he attended, what happened there up to the point where he left, whether there was an argument or a break up, what happened afterwards, whether anyone who was at the party found his phone etc.
I suppose there are privacy issues with, say, tracking whether Jack's phone moved in concert with anyone else's, but you do feel as though the police need to get around a table with his friends and just do some brainstorming on what was said, what people saw, what Jack's habits were, who lives where, what might be in this or that location or direction, etc.
JMOO