(not that this is not necessarily true for all segments of the teenage population- it only reflects my firsthand observations of upper-class, suburban, well-educated teens)
Social Media:
-Facebook: It's not like teens are in-mass deleting their Facebook accounts, however most are visiting the site less and less often. When they do visit, it is usually to post/look at photos or chat. Status messages and non-birthday wall posts basically are no longer used. Many younger teens are not creating Facebook accounts in the first place, this Freshman class is the first time I've seen many students without accounts
-Twitter: Twitter has become very popular, but there is still a large segment of the teen population that doesn't "get" it and has no interest in using it. I feel like it is very unlikely that Twitter will be able to win over these people.
-Instagram: A year ago, I would have said that Instagram is the most popular social network, however it seems to be getting less use in recent months. It's still very popular. The impending addition of ads have the potential to significantly turn-off Instagram's user base.
-Snapchat: I personally don't "get" Snapchat, however it is incredibly popular, and, contrary to popular belief, it is used more for selfies than sexting.
-Vine: Some people love it, some people hate it. Reposting "funny Vines" is popular, but I don't think too many teens are actually using the service itself.
-Tumblr: Used by a younger audience, and used mainly for porn.
-Tinder: Very popular on certain college campuses, but not at High Schools.
Devices:
-Smartphones: like any other affluent population, iPhones are the most popular, but Android phones are preferred by people who consider themselves more "geeky." The few teens I know who have gotten Windows phones have hated them, mostly because of the app ecosystem (or lack there of). There is a very, very minute segment of the teenage population that still swears by their Blackberry keyboards.
-Cameras: DSLRs (Canon or Nikon) are very prevent. Very few people have MILCs.
And another one.. They use facetime or Google hangouts and just leave the camera on. Is that a common behavior?