I've been performing a Tadoku and Tachou class in high school several times a year since I moved to Tokyo, and I was asked to continue it next fiscal year too. To my surprise, not only I will perform the Tadoku class, but also I will be allowed to use a computer room for the class two or three times a year, having a strong support from one of the English teachers. This is why I've been heavily into digging up new things on the net such as chat room, forum and social networks.
All these sites target teen, high schooler and college students.
http://www.teen.com/ ： biggest platforms for young consumers with appealing content and social utilities, along with dedicated fashion, health and beauty, sports and entertainment channels media content.
http://www.gurl.com/ : for girls
http://www.takkle.com/ : sports
I tend to be allured by more weired sites, but I can't introduced such sites during the class, so I should be stuck to searching for clean, safe and popular sites rather than secretive sites for nerd and Otadku...