is it ok to contact people on linkedin to find the name of the hiring person when applying for a job?

I've often been told that when you apply for a job you should not put dear/sir madam on a cover letter but should instead use the name of the person who is doing the hiring. however, on most job postings, they often do not include the name of the person you should send the cover letter to.

do you recommend using linkedin to contact someone in the company in order to get the name of the hiring person?

sometimes i find that when I look up a comapny on linkedin, I find that we have 2 or 3 connections in common, therefore it would seem that using linekdin would be a great way to get more information especially if you already have mutual connections.

what do you think?