do you know japanese manga "ONE PIECE"? in this manga, sailor are 仲間, they are not friend for another example, I belonged to volleyball club when I was junior high. During we are practicing it and playing it, teammates are 仲間. But when you be with them without club activity, they are friend(ともだち) 仲間 is used about a group that they have common purpose or goal.

http://dictionary.goo.ne.jp/leaf/jn2/163364/m0u/%E4%BB%B2%E9%96%93/ http://dictionary.goo.ne.jp/leaf/jn2/160395/m0u/%E5%8F%8B%E9%81%94/ They are almost the same as a meaning of "close friend" . but Nakama has the wider meaning than Tomodachi. Rarely Nakama is used to express not only good friends but also the others . For example , according to the above link , Nakama is used to express "same positioned people , same kind of something , labor union when it was expressed in Edo-era , in addition to the close friend. It is the explanation from dictionary but In my opinion , you should use " Tomodachi" to express "close friend" because Nakama sounds like the word spoken by punk-guys . Good Luck : ))

Nakama = colleague Tomodati = friend