Searching a group at "meetup.com" might be a good idea. There are many groups which Japanese who want to learn English or have communication with foreigners gather.
Or Hub Japan offers plans to interact with Japanese locals in "BE A LOCAL" page, too :)
You should go to Roppongi. That place is famous among foreigners and there are many bars and night clubs. Japanese people who want to communicate in English also go to Roppongi.