1. What country are you in? I know that in the UK there is a database of lost/stolen phones, so that you can report a loss. (Good that you have the IMEI, many people couldn't care less until their phone is gone, and by then it's too late.) The main service for this is
immobilise, which is officially supported/used by the police, in order to return missing property such as phones: if the police find a phone they check the database for owners, in order to get it back to you.
2. Report it to your mobile provider as well so that phone and sim card are locked.
3. There's not much chance of your getting the phone back, unless some kind individual finds it and phones you up -- unless of course the phone is already locked, in which case they would have to hand it in to the police, but many wouldn't. If it is found by the police though point 1 applies -- they find it in the database -- and you should get it back.