Social sites were designed as a great way to meet new people with similar interests, and are very good at this function. However, to assume that this is their only use is to take rather a short view of the potential offered by such sites.
The truth is that they are growing in popularity as a means of contacting old friends, contacts and schoolmates, as well as missing family members, and more besides.
As a larger percentage of the population make themselves available online, the long term benefits of these sites becomes more apparent for anyone who seeks to use them as a means of contacting old friends.
Here is a site about people search, social sites and more.