pining cat :(

[kallima]

I have 2 male neutered cats, both very keen on each other and who tend to hang around together all the time. one has been missing since yesterday which is totally out of character. they are both out during the day, but always come in at night. they both tend to come when called. I'm about to head out again to look for him.

since he's been missing the other cat, who is normally quite a demanding "feed me now" type, has gradually become very withdrawn and now won't eat, even treats. it's horrible watching him be all depressed and I'm scared he is going to pine away. is there anything I can do to encourage him to eat?