Why blogger posts can be deindexed?

I just noticed that my current number of indexed urls are lower than few days earlier. That means google has deindexed some of my urls. Whay this can be happen. I have started "blog posting" with my blog url, this is doing good in getting referring traffic, but not search engine traffic. Please give me some sugestions...

 

Have you checked omitted result option? It is at the bottom.

 

It may be because google considers some of your posts contents as duplicate content. That could be one of the reason why posts may be moved into supplemental index (and thus appear to be de-indexed).

 

Hi, What this option do, i didn't find, on which page should I find it?

Regards

 

where you checking them. note that Google does not show all the links.

 

Then what else is best use for google webmaster tools?

Regards

 

try to do deep linking.. my blog is a few years old and still all pages are still index.. just keep on gathering links..