If it helps, you're not alone - I do the same thing. I stop short of actually pulling the hairs out now, but at one point I practically had a bald patch at the top of my head, and it was a very hard thing to quit! It's been almost 17 months, and I still struggle sometimes.

Do you know what makes you want to do this? I find it gets worse when I'm bored or under stress, which is why I usually slip up at exam time.

Anyway, hopefully seeing as you've noticed this early (took me about four years to realise anyone else did it!), it won't become a problem. What I find helps most for me is holding something in my free hand - typing's good, too, you need both hands for that!