I mean social networking site.
Creating a social networking site can involve a lot of time and money depending on the way you want to go. There is free(with few features) and there is premium. The link will provide you the information you need concerning creating, hosting and managing social media sites. Also refer to this post for more information about social media templates http://www.techyv.com/questions/how-create-or-download-free-joomla-template-facebook.