I had my phone stolen and basically did the same thing. I didn't want to approach anyone for fear of starting some altercation. Wish there was a better way to go about this.

With my phone, if I had another device maybe I could have made it make a sound and then started a conversation with the person that way? I didn't know who exactly had it, although I am pretty sure I saw the person just walk away with it. Wasn't sure enough to make an accusation though.