HELP! Lost of Iphone...in need of IMEI number.

I lost my Iphone 4s and I need the iMei number to trace. Currently Im still tracing under Find My iPhone App using iPad. THAT fellow actually off my phone at my last location. So I cant detect until the mobile is on. Thus another way of solving will be through IMEI number which i need to hand it over to the police! How can i get the iMei number? It was swapped with Singtel as due to previous phone is faulty and replaced. So the box that originally does not have the new iMei. Can I use Itune? As previously, I did sync into iTunes before. Will it have the record of my iMEI number? PLEASE HELP ME!