Thanks guys. I am gonna explore BuddyPress.
Meanwhile would you please guide what me what if a plugin does not offer extensive features for the social network like blogs, photos, videos, music, events, groups, wall, forums, invite etc. I personally think that it is more feasible to look for open source social network code in core php and try to incorporate it to wordpress. Btw i am not sure what is the best (and the easier) way to incorporate. Anyways this will provide more flexibility to extend or modify the functionality as per the client's requirements instead of the plugin. May be i am wrong. In fact i am not so well up in wordpress and don't now much about how to use it the best possible way in such scenario.