use socialoomph. This one is a very good tool to find the targeted audience and to automatically follow and no follow twitter users based on some filters.
The only good one I have used is TwitterFriendAdder Pro but as you've said you've used this and had no results. There was a free eBook the other day that described using email grabber that search all social networking sites for emails to build an email list then just add the list to your friends and in no time you will have thousands of followers. I suggest you maybe try searching for this ebook in the freebie section
I don't bother with those tools - they just end up adding spammers and people who couldn't care less about what you have to say. I prefer a more manual approach