Really! As internet is growing, people search is getting easy or it is lot more easier than before. And social networking sites are a boon for searching people on the web. As for example I found many of my friends on Facebook. This is the reason I started loving Facebook otherwise I am a twitter fan for real.
So searching people on the web should be starting from (1) Facebook_Search in this era. Facebook is data of 750 Million people, most of the people are on Facebook because of their friends are doing interesting stuff there. But sometimes only Facebook is not enough because so many people I know do not like to expose themselves on Facebook or any similar social network.
After Facebook I think (2) twitter_ is to be considered before any else. I think twitter is still ruled by intellectual property of the web. A great source for search great souls.
Also Google search is still useful and relevant for people search before starting special search.
There are many people on the web who like to only on selected places so it is recommended to search on various social networking sites.