Nightlife in Helsinki

Hi! I've recently returned to Finland after years abroad. Don't know a lot if people in Helsinki and I'm completely out of touch when it comes to nightlife here. And I have an international (Internations member) friend coming this weekend who I'm supposed to show around! I'm wondering if Internations members are meeting up more informally, during the weekends, to have a beer etc? Or if I should join a particular group, please advice...