I checked backlinks of my site using "link:www.sitename.com" in google but google does not shows any backlink. Before few days it was showing 13 backlinks for my site now it does not suddenly all backlinks lost :(
anybody know what is reason of this? is my site suffering from penalty of google?
This isn't entirely unusual. For some time Google has been making it difficult to see all the backlinks you have.
You used to be able to simply use the link: command and see all links, now this seams to produce fairly strange results, as you have seen it changes from time to time.
Some suggest this is to prevent site opperators from beign able to locate all links that point to their competition. Back in the day if you where in competition with another site, you simple found all their links, and send link request emails to them. This may have given some sites an unfair advantage.
link: command on Google and Yahoo has got one interesting peculiarity in that if there is a page redirecting to another page on your site, then backlinks of that original page will be deemed to be your own backlinks, ie:
example.com points to example.org, which redirects to actually your own site - example.net, so in this case example.com will be deemed to be a backlinks to example.net.
So, if there was a page that had plenty of backlinks but it suddently stopped redirecting to you then those backlinks might be deemed to no longer point to your site.
This will not necesserily explain what is happening in your case, however this behavior is something that does not appear to be well known, at least it was not to me until recently.