The best and by far most impressive thing you could do would be to write an actual physical letter (not an e-mail): something that shows you are willing to put genuine effort behind your campaign to encourage the network to extend the show. Even better, you could do the same, not only to Disney and the show's creators, but to its sponsors as well. Networks and others respond surprisingly well to letter-writing campaigns. Be as upbeat and creative as possible. Remember always to be respectful, and NEVER to threaten. If you write the sponsors, always suggest that you have patronized their product after hearing about it during the show. Petitions, in my experience, are practically useless.