"I couldn’t even get my own teenage daughter to look at Google+ twice, “social isn’t a product,” she told me after I gave her a demo, “social is people and the people are on Facebook.”"
Additionally, MySpace killed itself by pursuing the wrong objectives. Facebook didn't kill MySpace, MySpace killed MySpace.
Thing is, class divisions are a fact of life. If your goal is to pursue a more just society, it's worth trying to minimize them (though even then, you need to acknowledge them before you can do anything productive). But if your goal is to get maximal user uptake for your new social network, it's worth exploiting them. They aren't going away, and if you don't, someone else will.
A lot of Web startups have actually had the byproduct of significantly lowering class divisions, eg. Google gives important information to people who would not otherwise have had it, Twitter lets people organize who would otherwise have been divided & conquered by oppressive regimes. But to get there, they need users, and one powerful way to get users is to be seen as a status symbol that makes one cooler than their peers.
MySpace's ad deal with Google encouraged a site design that was anti-user. Facebook developed their own ad platform that allowed them to extract value from data that only Facebook has and that third-party networks couldn't get value from because it's so specific (like where you went to university).
But as much as the movies would have you believe Facebook won on "coolness", it won on old-fashioned better product decisions.
Once Facebook understood the appeal the site had to the general population, they realized that it would be better for them to create an ecosystem where network effects were optimized for the decentralized user base as a whole rather than the centralized subnetworks that made the site take off in the first place. At each step, they focused on what worked for the users at the time.
Google+, on the other hand, really did deliberately start out as an exclusive network, largely for people in the tech world, and it hoped to quickly transform into something with universal appeal. You can draw your own conclusions about how well that worked.
Google+ is only cool for geeks, if even that. I'm not sure what to do with Google+. The technical folks I work with aren't sure. The non-technical people barely know it exists.
So it's probably too early to tell if teens will use google+.