Is there any group of travelers/backpackers I can join?

I live in Minneapolis and was looking to travel from Early august to Early September. I know about couchsurfing.com where you can look for people who'd be willing to accomodate you. But is there any legit website where I can find people who'd be intersted to go on trips to diff. places (i.e. South America or Europe)? Lemme know. Thanks!