How to manage Social media user accounts for employees

We have employees that come and go . It's been an difficult to manage the company social media accounts (Facebook, twitter, Linkdin, .......). I am not sure what others are doing out there. I would be willing to pay for a service that could be a single point of user account management. ( free preferred ;-)  ) .
We are also constantly worried about  people leaving the company and us having to after then and ask for the account info .