Hey Next1m8, Sorry to hear of your current troubles.
For me there are several things that have my alarm bells ringing.
Not returning calls or messages.
Not turning up to work for 3 weeks.
His GF blocking you on FB <<< This is the biggest alarm bell.
If all is well, then why has she blocked you? Obviously they have something to hide.
The whole not turning up to work is also another big alarm bell. Now I'm not accusing him of anything, but crystal meth will do this to a person. They just disappear. They live in their own world of crime, thieving whatever they can to get their next hit. They have no mercy on who they will rip off, they will even rip of their own mum.
Go to the police IMMEDIATELY. Report it as stolen. Do not wait another second. This bloke is no friend of yours and in my opinion there is only one place he should be >>> Jail. I hate thieving pricks, they have no place in society. If people have a habit/addiction, get a job and feed it with your hard earned wages, not with others hard earned.
I hope all turns out well, but by the warning signs I have seen, well....
Take a drive past their house at night and see if the lights are on, but I would be very cautious about approaching them, especially on your own.