This is the second time my mobile is lost. Well this time it is clearly a theft. I kept my Xiaomi Redmi 1S for charging on a table nearby a window. Somebody somehow opened the window and picked the mobile during night when we were sleeping. Though we woke up hearing some sound, it was too late; the one who picked my mobile has left by then.
Without wasting much time, I called the customer care center and requested for temporally blocking my mobile number which he accepted after verifying my personal details.
Now, the next thing is to inform police. However, from my previous experience, I was sure that they will not help much. Maximum they will do is nothing but issue acknowledge for lost mobile reporting. They says, the IMEI number is added to the tracking system and if someone use the mobile it can be tracked. But, still there is no information about my Sony xperia U which is in tracking system since two years. I have found the news here about arrest of person who used to modify IMEI. So what I think is, the people who steals the mobile would approach such people, change the IMEI and then either use it or resell. So, the tracking systems will not be able to find the mobile phone. Below line is from the news source.

Accused, who is a software engineer, was arrested and charged under the IT Act for using technology to change the unique IMEI number of mobile phones

Now, for getting a duplicate Sim-card also, acknowledge from police station is required. This is because, I have ported my number from Vodafone postpaid to BSNL prepaid. And for getting new sim for prepaid, acknowledge is must. Also I think it is necessary to report the loss to avoid any misuse/abuse of the device.
While searching the Bangalore police website, I found this website of Bangalore police. In the page, there is an option 'report lost'. A screenshot is pasted below.
For reporting, we will have to first search in their partner site Lost Click Found. If our mobile is not in the list, then it will give us option to reach this page(Police report of lost item) finally report to Bangalore City Police site. Here there are lot of categories. After submitting we will get option to download the acknowledgement. I have pasted screenshot of my acknowledge below.

Acknowledgement downloaded

However, in the form, there is no option to enter IMEI number. So, I mentioned in the comments column. Since, the IMEI number is not specifically asked, I have also personally went to the nearby police station and informed so that they will add the IMEI number for tracking.