Your company's employees are participating in social media on your network. You may encourage the practice, or you may discourage it, but unless you run a "1%" locked down environment, it's happening. Probably as you read this post.
Social media can be a great communication and marketing device, but it also presents a wide range of risks for your company, of both inappropriate disclosure and IT security breaches. The best bet for any company is to thoroughly train its staff about best practices for using social media.
"Socializing Securely: Using Social Networking Services," by the United States Computer Emergency Readiness Team, offers a wealth of advice for any user of social media services like Facebook and Twitter. The 5-page PDF, which is available free to IT Business Edge members here in the IT Downloads library, is ideal as a quick training pass-around to your staff.
The report starts off by listing the various threats posed by social media: social engineering attacks, identity theft and good old-fashioned viruses. When the entire user experience is based on building trust with people whom you've never actually met, there will always be folks looking to abuse that trust. And even with people you do know personally, the implied anonymity of the Web tends to make even well-intentioned folks a little reckless - a quick status update about how stupid your weekly team meeting is not only hurts your own professional reputation, it makes your company look bad.
The report lists two steps that, in a corporate setting, fall under the IT department: Keep anti-virus solutions and OS and application patching up-to-date.
It then goes into greater detail about best practices that you will have to count on your users to employ.
Again, your best plan here is training. The US-CERT report is a great starting point.