I hate weekends too.... all week I'm busy with school, acquaintances and schoolwork... weekend hits and I can't even focus on assignments due next week, I sit here and either type on my blog, this forum, or play World of Warcraft.
May I suggest World of Warcraft? You talk to people like here but mostly just to get objectives completed. Or if fantasy games aren't your thing, any video games at all? There are some really good ones out there that you can go online and play with other people. My guild on WoW actually has a facebook page and does in-real-life meetups (one is upcoming this month).
Organized activity is a great suggestion too-- though I would struggle with committing to something every weekend and build up anxiety about returning if I happened to have a meltdown and miss a scheduled event. Online it's easier! "My cable/power/computer went out", My dog crapped on the carpet and I had to go, etc. etc. tons of good excuses, no one will care.
If you don't like video games there is always stuff like "farmville", "angry birds" etc.
Or perhaps you like to write, read, draw, paint, etc.? Those activities when I do them always get me engaged with other people: I paint outside with watercolor when it's nice, I read at the library or coffee shop where sometimes people approach me, and writing gets me comments on my blog and other interaction over emails, etc.
Just a few suggestions, I don't know you but hopefully this speaks to you somewhere.