More and more people and businesses are using social media as a way to also professionally network. The most common are:
Here is an article on Mashable - How Job Seekers Are Using Social Media for Real Results - describing how using social media strategically can be a great way to secure a job.
There are certainly some advantages but also some cautions one should be aware of before setting up an on-line presence. Take a look at this article on Career Builder - Not getting job offers? Your social media could be the reason​.