well, i think i understand your problem here. for the conversations here usually you don't usually need a large vocabulary. i think you should ask people to talk to you about the specfique subjects you want to broaden your vocabulary in. Maybe someone might be in the mood to talk about such things as "business relations in a globalized world", "human resource management", "environmental care",.... or whatever interests you. these don't have to get into long discussions. 2 to 4 mails exchanging ones opinions would already be helpful i think. another useful tool for this might be the notebook function on italki. just force yourself to write short essays about the subjects you're interested in. you'll have to look up a lot of words in the beginning, but doing so bit by bit you'll get them back to your active vocabulary.