Winklevoss twins: Bitcoin will be bigger than Facebook. The brothers, two of the most influential players in a new generation of investors, say bitcoin will encourage financial openness.
http://www.ahametals.com/bitcoin-bigger-than-facebook/
http://www.ahametals.com/bitcoin-bigger-than-facebook/
Sorry but they are completly different things Facebook is a social media obviously and Bitcoin is a DIgital currency which worth month money you definitly can't compare them between each other . but if you mean from the numbers of the users and fame then I guess you can say that . not anytime soon because some people are just not open minded and will think that bitcoin is a scam
Maybe in 10-20 years let's say 
Even if they are different things you can still compare them in terms of adoption, success etc. Also new technologies like MaidSafe will make decentralized facebooks.