As a Muslim,there might be a certain thing we can or forbid to do. Not like a Chinese, Hindu or Athiest, they are able to do everything even not all, but they are more free than us. What are we concern here is about the issue of covering aurah for Muslims.
Facebook is a place where people can upload their pictures for free and unlimited. So, many of young Muslims nowadays especially ladies, uploaded their photos in variety of styles with reason of fun. The question is where is the feeling of shy for a young lady? They seems like have no knowledge about aurah. This might be a challenge for young generation to avoid such things and so become a good Muslim.
Furthermore, they are people who use Facebook as a medium to find a life partner. Yes this is correct but some of them use it in a wrong way. Islam forbid us to have neither boyfriend nor girlfriend. So for those who are less concern about this matter, they have no issue on using Facebook to do such things. Again, it would be a great discussion regarding this.
Besides that, limitation in friendship between boy and girl must be considered as you can't go beyond the limit. Currently, social networking not just Facebook, has been being a place for discussing a sensitive issue such as porn by irresponsible people. Many pornographic items are available even though Facebook's security has forbid it. But we don't have any idea how this things could happen in this site. Plus, such people don't put those items in private-they mean it!! So it would be tough for parents to guide their children nowadays because this site(Facebook) is easy to achieve.