Twitter lends itself perfectly for multiple people to use the same company account.
It is a nice touch for each person who uses the account to sign off their tweets with their initials. Whilst giving the company account a more personal touch, this also means that customers know who they have spoken to and are able to connect via other methods to the company and ask for the person they want.
Customers like continuity, especially when it makes their life much easier – and as a result makes it much easier for them to buy your service or product!