When you as a freelancer do your best at all times, gradually you will build a solid reputation for being no-nonsense and reliable.
I'll let you in on a little secret on how business is conducted in the corporate world. With the meteoric rise of networking sites like Facebook and LinkedIn during the past several years, many employers have used them to screen applicants.
Now, employers want to make sure that a potential hire has what it takes to be a team player and the patience to ease himself into the company's culture. So should they spot any form of indiscretion (e.g. lewd or questionable behavior shown in photos in the accounts of a potential hire), employers will not hesitate to pass him up no matter how strong his credentials.
As a freelancer, you most certainly can use Facebook and LinkedIn to build your platform. But be selective about what you choose to upload.
If you're a graphic artist or illustrator, make sure that you have your best artworks laid out in a way that it will attract a lot of potential clients. If you write online articles, provide links to the ones that have most recently been published.
You may also allow a certain level of interaction in your Facebook account, where you allow your work to be critiqued by your peers. But you must make sure that comments are moderated. Otherwise, you run the risk of dealing with hecklers, or even worse, cyber-bullies.