Who runs the pages of companies on twitter and facebook?

[Q]

Do people from the companies make posts and tweets or
do they hire people to run the pages?

[Peter Nikolow]

It dependent from company. Almost all companies use internal team of SMM experts (Social Media Marketing) that run pages and coordinate efforts with marketing team.

There is cases when external companies (SMM agencies) run company accounts under agreement.

[Susan]

To run the pages of companies on twitter and Facebook, company may use the internal social media marketing expert or they may hire social media marketer from outsides.
simply,to run the pages effectively on any social net working site such as twitter, Facebook a company need expert social media marketer.

[Brandon Leibowitz]

Social media marketers run those pages and you can find a jon on many job boards by searching social media community managers