I have been trying to sort this out for a while, how to find my Facebook friends who are on Twitter and add them. I have searched and found little help and ideas. Also the FB application for doing this only works if the friends are also using the application.
However I would suggest trying this idea. It is not exactly perfect but it did work for me.
1. Log into Yahoo or set up a new account
2. In the contact options import all your Facebook contacts into your Yahoo Mail address book
3.Log into Twitter
4. Select find friends and then import from email account
5. Choose Yahoo
And then it will prepare a list of contacts who are on Twitter from all your contacts including your Facebook ones.
Almost too simple....