Considering you lost the phone, the cops would have most probably registered an NCR (Non Cognizable Report) instead of an FIR (First Information Report)? Usually no cop takes up an NCR for investigation, which is why they prefer registering it over an FIR even when one is robbed off his phone. You might have to push them to help trace your phone. Remember they are already overburdened with cases of murder/rape/dacoity and searching for a lost mobile may not really be high on their agenda. I hope they make an exception in your case, but if nothing works out, you should at least report the IMEI so that the phone can be rendered useless.