I've returned phone to event organiser before when I found one.
Was at Sentosa, many years ago.
My friends have lost their phones, reported to police and given the
IMEI codes. Didn't get to retrieve the phone, but I think it's
better than not doing anything.
Cause at least the phone cannot be sell. And at every legitimate
shop that's dealing in 2nd hand, they'll log the phone's IMEI code
for their sales and that log is being screened occasionally for
lost phone.
Lastly, my condolences to TS. Hope you does find back your
phone.