Blogging and teens

So I'm just at the beginning of this particular online area. I would like to figure out how to integrate some blogging into our creative writing workshops....but I'd like to make it less about just entering casual blog entries, and more about getting the students to deliberately create a theme-based blog where they write about some area or interest where they have some expertise or at least curiosity. I know this is perhaps a more formal way of looking at it, but I would like to challenge the students to really create something with their blogs, instead of just typing up their feelings or more casual entries.

I've been researching a variety of educational blogging sites, but I think I need to do a lot more research! Wow. Who has time for all this???