I dont really see the connection. You may have a facebook account and not be able to make any good use of it. Just like any other social networking site, it depends on how you use it to promote yourself.
Depending on the kind of online career you aspire, you should select a social networking website.
I use facebook to communicate with my friends and when I write articles or make a new website I post it on my profile.
It might be important to have a facebook page which in turn providers good opportunity for promoting something.. But at the end, it all comes down to having a skill or a product that people might be interested in.