Is it normal for a 12 year old to still use a pacifier?

No. It might be something that helps him feel less anxious I mean I can't think of too many other reasons why he'd be doing that. I don't know what to do for you though.

Tell ur parents 2 get the dentist 2 explain the affects it could have on his teeth the next time he goes.

Not normal, but not a big deal. Some twelve year old's do much worse. Just be glad that it's only pacifiers he's sucking, not the tip of a crack pipe or the head of some stranger's d*ck. He'll stop when he's ready to stop, and so long as he only does it around you, it's not even embarassing.
Leave the poor kid alone.

Tell him to try chewing gum instead...

I was still chewing on a pacifier around the house when I was like 6, because I just like chewing on things. But I later found out that my mom had taken my pacifier and claimed I lost it, because she thought I was too old for one.
So now I just chew pens and rubber.

Try getting him out to the park an such more, play games with him where he doesn't use it or forgets about it then if your able to, I'd just pitch it to be honest. Yes it may sound harsh but unless you plan to ask a doctor about it or just let him eventually stop using it I don't think there is an easy way for something like this to stop.

Or you could try what LosFounder suggested smear something distasteful on it, but he will probably wash it off if he's that obsessed with it.

He needs to seek professional help. He seems to have an anxiety problem and he needs to learn to deal with it using healthier and more socially acceptable means.

No! He's gat an oral fixation, an needs counseling. It probably shows deep insecurity. All of you may have to go for a few sessions though, because he's going to need youtr support.

I was a thumb sucker for a while back in my days. It was a great source of comfort. My greatest actually. His pacifier is probably his. Granted, it's not normal. Just smear rat poisoning on his pacifier. But make sure it's organic.