Who should I send my resume too?

I’m currently unhappily working on a helldesk and hoping to land a first level systems engineer position anywhere but where I am working now. I plan to start targeting companies that I would like to work for.

Un Qestion:
When sending out a resume to a company that hasnt listed an opening, who is the best person to send it to? CIO, IT director, human resources? How could I find out who on earth that person is?

Any help or advice on this or any other job searching strategies would command a thousand thank you’s.

Regards,