If your buddies are not online or at least are not showing up as online you have to enable that offline buddies are shown.
To do that start gaim, connect to aim/icq.
Go to the Gaim menu - Buddies - Show offline Buddies.
Double tap a buddie as if you wanted to start a conversation with him/her.

Now you have the chat window opened.
Go to the Gaim Conversation menu. Select Conversation - Remove.

And you just removed the buddie from your buddie list.