It's called a run-on sentence.
Seriously - split that sucker into two. No, three.
What you've currently got is not well-written at all. If this is written by people who are looking to publish in English, then they are going to find out the hard way that they are not on top of things at all.
I need to have a gimmick. Mine is time portals, and balancing our readership. Facebook attracts an older audience, Twitter, a younger one.
You could even split it into four separate sentences by replacing the comma before Twitter with a period and adding the word 'attracts' in place of the comma after Twitter.