Tyler Cowen asks why the fascination with Vampires and comes up with a few compelling reasons.

3. Vampire stories offer a platform for exploring the theme of pure, limitless, and eternal desire, yet without encountering the absurdities that might result from planting that theme in a realistic, real world setting, such as a man who loves cheese studded with raisins above all else.

4. Vampires play "hard to get" with women and they (for a while) embody Old World ideals of chivalry, in a plausible [sic] fashion.  Yet since they are fundamentally different beings, we can enjoy watching their strategies while simultaneously distancing ourselves from them.

He misses the most central ones: blood lust and danger. You’ll note that teenage girls are a big part of the vampire demographic.

A vampire wants you, in the absolute worst possible way. And, once he has you, at best you are transformed forever, at worst you are dead. This is a clear metaphor for the most pressing issue in young teenage minds.

Vampires are also tend be strong, wealthy and of high status. All of that in a package that is conveniently and familiarly, young. They are often literally 400 year-old aristocrats in a 18 year-old body.