Do you know a teenager who's suffering at secondary school because they're unpopular? Get them to read this essay by Paul Graham called Why Nerds are Unpopular. It won't help them become the social centre of the school, but it will help them understand why they're being persecuted, and why, in the long run, popularity in school is meaningless. Although it's written from an American perspective, and looks at the American High School social hierarchy, believe me, a Scottish secondary school is no picnic for a bright kid with glasses, severe Tourettes, and all confidence and self esteem expunged by the system.
I wish I could have read this thirty years ago. It might have acted as a signpost to better things.
So read it. Then, if you do know someone struggling in that situation, e-mail them the link, or print it off and give it to them. Don't say "I know what you're going through." Just give them the essay. If they want to talk about it, they will. Then, if you've been through the same hell that is secondary school, tell them, "I've been there."