Posting on his guestbook will typically get a response within a few days to never. If it's a serious inquiry, he'll likely respond, I guess; seems to depend on his mood, though, honestly.
If it's about darkSpyro, he does usually respond to questions in the Site Help and Suggestions section.
Now, he does have a Facebook, but I don't know which one would be his.
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"You already said that." - Veruca Salt, Charlie and the Chocolate Factory (2005)