In order to answer that question we first need to differentiate these two social networking giants, and don’t make the mistake in thinking that Linkedin is not a giant, it is just under Twitter and Facebook in terms of popularity and usage.
What are they and what are they used for?
Non-business users on facebook use the site for seeing what their friends are up to, sharing pictures of cats, keeping in touch with friends, etc. Business users on facebook have the opportunity to promote to said users by way of ads or if the user has ‘liked’ the business page, by having their company’s posts show up in the user’s newsfeeds. Facebook takes advantages of ‘knowing’ all the interests of its users therefore it enables business users to target ads specifically to those interests.
Every user on Linkedin has his profile page which is basically a professional CV. User’s sign up to Linkedin in order to either get hired by other users who are looking for employees, or to connect with former classmates and colleagues. You could call this a ‘passive user’. Active users are those who use Linkedin to actively search out people for hiring.
Facebook is used to promote to your consumer base or get new potential consumers. Linkedin is used to find employees or useful business contacts. As you can see those are two entirely different activities therefore neither website can replace the other.
The very structure and nature of Linkedin differs tremendously. You will find no ability to post photos (aside from your profile photo), nor can you have a blog, or embed video on your friend’s page or do any other facebook-ish features. However you can search out and add ‘friends’, (they are not called friends, but are called connections) the acceptance/approval process is the same as on facebook.
Although it is free to search for jobs Linkedin will charge $145 to the company who wants to post a job listing. And around $100,000 a year for company who want their special advanced search for finding employees.
The conclusion is quite simple: use Facebook for promotion and Linkedin for hiring.