I'm so sorry that Riley decided to take a trip.
Don't give up hope. Can you find time to sit outside for a while reading or listening to music? Call his name every now and then and he just might show up looking for some lovins.

This website http://www.petrescue.com/petlibrary/...st-cat-or-dog/ has many suggestions.

If he's not home tonight, I would take action. Sadly, with Kuhio, we learned to late.