I believe you have two separate but linked problems here, smoking and raising allowance.
If you are worried about your son smoking, talk to him about smoking. Ask him what he thinks about it, what he thinks about his friend smoking, etc. Talk about why you don't want him to smoke. Teach him.
Realize that if he really wanted to smoke, he could do it on his current allowance. He could even just bum cigarettes off his friend. While restricting his cash flow makes it harder to smoke, it wouldn't be impossible. Remember that one day he will get a job and have much more income, income that you won't be able to control. And then if he wants to smoke, he will. But if you teach him about it now and he decides he doesn't want to smoke, a change in income won't magically make him want to smoke.
1Basically, don't use allowance restrictions as a way to stop smoking. Don't use allowance as substitute to being a parent and talking to your child about this. If you are worried about it, address it directly.
As far as figuring out allowance goes, I wouldn't worry so much about what his friends get. Talk to your son about what he spends his money on. Ask him what he would like to do with the extra money. If all of that sounds reasonable to you and you are comfortable with it, increase it. If you feel like it would be excessive or inappropriate, tell your son that and why. Be willing to listen to his arguments. If he makes valid points, acknowledge and consider them. Make this a discussion, so you can both see each other's side of things. This also makes for an excellent teaching opportunity about how family finances work and what are appropriate uses of money.
1 I didn't intend for this paragraph to sound like a criticism of you or your parenting. The fact that you worry about this kind of stuff shows you care and are trying. This was meant to be bit of a wake up call, so please don't take this the wrong way.