Hey fod, here's my bigger boy ideas. I'm just one woman talking, so feel free to ignore. It's going to kill you to do it, but big breath, and .....
Give back all the confiscated stuff. Stop any punishment whatsoever until you have a clearer idea of what is going on behind all this. Sit him down. Hug him. Tell him that you totally want to kill him right now for how scared he is making you, and how powerless you feel right now, but that you are his mum, you trust that he is essentially a good kid, and you know that he won't have changed inside, whatever his behaviour is right now. Tell him if there is anything he needs to tell you, you'll listen, and you'll try not to scream at him (and that's the hard bit, because you might want to throttle him for whatever is going on right now).
Not doing the homework is a bit naughty (and obviously scares the crap out of us parents), but there might be lots of reasons for that. Not coming home and not telling you is rotten. That's scary, and it's not fair of him to do that. Tell him you're making a distinction between what's just pain in the ass behaviour (homework - that part can get sorted/caught up when the behaviour stuff is fixed), and really not ok (not letting you know where he is, because you love him, and need to know he's okay). Hug him at this part too. Maybe pass some biscuits over.
Tell him that you have no idea what's going on for him, and that you know it's really hard to be a 12 year old. Say that you know it's probably harder for kids now than it was for us when we were 12, and that you know there is more bullying, more drugs, more sexual abuse (and yes, you need to say all that part), and on top of that you know he might have all sorts of thoughts about how the family is going to change with a baby in it. Do more hugging now.
Tell him that you're not going to try to force him to talk right now, because you get that he might not know what to say right away, but that you love him, and you're totally on his team, whatever is happening for him, and you'll do anything you can to fix it, whether that's changing schools or whatever (you probably don't need to actually do this, but it lets him see that you are thinking big here if he feels he needs you to get that it's something serious). More hugging here. Then walk away (unless he's ready to talk).
Sending huge parenting hugs xxxxxx