A shared web hosting plan is the last one you should think of.Since you are planning to launch a social networking website, you are bound to receive high traffic gradually.But, you cannot predict it as to when your site would receive high traffic. Imagine if your site is hosted on a shared server and there is traffic to pooling in and your sites goes slow, for sure it would affect the visitors, they would simply leave your site and hunt for a faster and better performing website somewhere else. Therefore, it is recommended that, you either opt for a medium ranged VPS with over 512 MB RAM or a starter Dedicated server.