Not that I know of. Letters don't get to him, though - if you write to him, it will be thrown into the trash.
(Information received from someone who knows him personally. No, I can't tell you who, because then I wouldn't be getting any more information.)
You could try writing to Steamroller Productions, but I doubt you would get an authentically signed photo from them, if that's what you're after. Usual practice is for the office staff to sign them before sending out. (And this doesn't just apply to Steven, before the screams from the usual chorus go up - it's a standard practice among actors in Hollywood, that office staff and assistants sign photographs on behalf of their employers).