Employees may not have good content to share about your jobs. I've sat with several companies in San Francisco that use Jobvite's Publisher program. I am hearing that it is a struggle to get employees to promote it on their social profiles. It is a struggle in the order of employees only using it an average of 10% of the time based on what I am hearing.
Why is it that you cannot get people to use it? Look at your Linkedin news feed, and click on a shared job through Jobvite, Bullhorn, or the like. You will most likely see an uninspiring paragraph about the job that was written 6 months ago. Now ask yourself, how often would I be hitting my entire Linkedin or Facebook friend list with a message like that? Not often.
My point is that content matters. Give your team something fun and inspiring to share. Give them something that people will actually "like" on Facebook, and shows off the job. Include pictures, sound, videos, or anything that will visualize what it is like to work at a company.
Companies and their recruiters are using all types of tools to connect with candidates and show off a cool careers page. Many are then falling well short of asking employees to share relevant and engaging content with their networks. Change the status quo, syntax-laden job share and you will begin to delight candidates and inspire sharing!