It might be worth mailing them a poster and asking if anybody remembers seeing him around Christmastime. Depending on where the ward is, it's probably not that common to have strangers drop in for services.
This is something we discussed (and suggested) earlier: having the LDS Church do a "broadcast email" to all of their churches, with the alert about Steven being missing and including the poster as an attachment.
That way, they could forward it to their members OR at least post it on the bulletin board.
The website we non-members have access to, doesn't have email addresses.
BUT....we have some very good LDS members here who could start that ball rolling, because they'd know exactly how to start something like that.