I think social network is an effective way for us to develop new relationships, because it is time-saving. Besides, speaking on net is easier for most of the introverts to break the ice with the person they first meet.
But if we want to build the relationships true and long, we can't only rely on social network. Face to face interactions and conversations are important to maintain a true relationship. Words on net have no temperature, but a smile or an embrace can indeed warm everyone's heart. Also, things on social network are not all real, face to face interactions can help you to identify the true friends.