Facebook has earned its reputation as an AOL-like walled garden by keeping most of the content generated within Facebook hidden from those who haven’t logged in.
Not only does a login screen stop general Internet users from viewing Facebook content without logging in, it also impedes search engine indexing.
Currently, Google can index:
a limited view of Facebook user profiles“Fan” Pages, including user postsFacebook comments left on third-party sites
At one point in time, search engines were also able to index many Facebook groups, but this does not appear to be the case any longer. I should also note that users may change a privacy setting so search engines can’t index their specific profile.
See on searchengineland.com