Who allows access to Social Media sites at work for sales force? Can you direct me to any research or proof that these sites are risky from a malware perspective?

I would refer you to news searches in Google for a start. Not a research project, but I'd say you can hit a malware site more often from an email link than social media, but the latter could easily have malicious links just like an email or another web page. There is always a risk, whether it's more or not, I wouldn't think so.

Train staff to work smart and keep protections (firewall, anti-virus, etc.) updated on the systems used.

There have been reports recently of malware being contracted through links found in Facebook posts. It typically spikes this time of year, with lots of "favorite charities" linked in posts.