manish_iitg - Please note that per the Google Forum Charter
[webmasterworld.com], we do not allow you to mention either the name of your site or the query you searched for in Google search.
Apparently, you are not ranking for your site name where used to rank. In particular, you feel you should be ranking on your site's own social profiles, etc, in positions 3 through 8. While very often you should, this is not always the case.
Possibly, the problem is related to the url change you mention, where you changed the URLs of your inner pages and set up 301 redirects. Can you tell us roughly on what date you made these changes.
aakk9999's explanation of your making such a large change during the Google "honeymoon period"... or a Google algo change... is very possibly the explanation. Another possibility is that there may have been some errors in your redirects, or that the redirects are recent enough that Google hasn't yet sorted it out.
It may also be, if you expected some of the pages to be from your own domain, that your site has been hacked. Hackers often cloak their work to be seen only by Googlebot, so you will need to use "view as Googlebot" in WMT, or a user agent switcher, to see if your pages have been changed.
A PS regarding the social profiles etc that have disappeared from page one. Have they dropped to a lower page, or have they disappeared entirely? I'm thinking that if you'd built links to them and they disappeared entirely, it may be that you'd built too many links to them with the same anchor text. That's an unlikely possibility, but I thought it might be worth checking.