LinkedIn is an essential tool for the business professional. Largely, that relates to the "business to business" professional. It is where sales people go to engage potential clients, and the general public will use it to find a job. The business community will use it to fill job openings and gather intelligence about their competition (at least, they should). Facebook certainly has a business component (What are they worth? A billion dollars or something like that?). However, you don't search for recruiters on there. But here is a good point: Recruiters will certainly look for you. Specifically, they will look to see what you post, what language you use and how you present yourself. If you think you can avoid detection by changing your last name or using a false name, you are fooling yourself. For both platforms, don't say or do anything that you are not willing to say in other environments.