Not used it myself but what about tweetdeck?
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https://dev.twitter.com/discussions/4766
Automated responses to new followers is discouraged. See our automation rules at:
https://support.twitter.com/articles/76915
Technically, to accomplish this you'd want to use User Streams to monitor new followers in real time, then issue either a statuses/update request or direct_messages/new request depending on how you wanted to communicate with them.