Company can search about a account by their own for security reason and I think finding a social media is not so difficult task in the digital world. But company don't have the right to force to share the social media handle. It should be an optional. If employee want to share, they they can share it. But again if company ask for passwords, it's against the law.
Hehe... asking for passwords is taking it a step too far. That's definitely an invasion of privacy. And it's definitely against the law.