Reddit mentions of The Big Questions: A Short Introduction to Philosophy

This might be heresy, but if you're getting started with philosophy it might be easier to open a philosophy textbook that touches on a wide variety of philosophical writings without actually getting deep into one. That's how most of my lower division classes were.

Robert C. Solomon's The Big Questions: A Short Introduction to Philosophy convinced me to change majors from engineering to philosophy. (Note, if you click the link, that there are vastly different prices for different formats, some are out of stock).

Alternatively, you could start on Stanford's Encyclopedia of Philosophy and start with some basic topics like causation or logic or ethics or something that you're interested in, and then just go from there, looking to see who the big names are in the topics you're most interested in.

Good luck.

EDIT: fixed link.

The important thing is to learn philosophy. If you don't know how to form thoughts, you don't know how to understand anything. Since you are a libertarian, I assume that you at least have good instincts about logic, if not, you have already been taught some level of philosophy by yourself or somebody else.

http://www.amazon.com/The-Big-Questions-Introduction-Philosophy/dp/0495595152/ref=sr_1_2?s=books&ie=UTF8&qid=1332136524&sr=1-2

Great primer for a young person.