There are more than one billion search queries on Facebook each day

"It’s no secret that Facebook is trying to get the most bang for its buck from its search bar. Companies are throwing money at Facebook trying to leapfrog competitors via sponsored results. Zuckerberg said the company is intrigued by what it can do with search, noting that there are more than 1 billion queries through the social network each day. He wants the search engine within Facebook to aid users who want to know things such as which restaurants nearby their friends have favorably reviewed and who has worked at a company they may be applying to."
Source:  AllFacebook, 11th September 2012