Without you having registered the find my iphone app, the chance of recovery is very slim. The next best thing you can do is call your telco, who would have your imei number and ask them for the imei number and tell them it's lost. They will deactivate your sim, but tell them do not deactivate your phone coz you would need it if the guy who picked it up insert his own sim card and the sim registers on the network. Tell your telco to inform you if the imei gets registered on their network, they will have the guy's phone number, but would need a police report to release the detail to you. Call apple and tell them the imei number and your apple id and fax in a police report if needed to release more details. I have read occasions whereby apple was able to trace the user's ip address when the person did a sync on home PC. With IP address or even email, you would be that much close to getting it back.
You have to accept that your things are gone and the good thing is that with apple's iphone being notorious for being easily tracked and the person who picked it up having no clue whether you activated the findmyiphone app, the first thing he would most probably do is do a factory reset or a hard reset to wipe out everything. If he insert his own sim card or try to sync your stuffs to his pc, then telco and apple will know for sure.