I need to find the location of a cell phone used by one of our employees

What type of phone?

Here is a wiki link of all the phones

http://www.wikihow.com/GPS-Track-a-Cell-Phone


One thing to remember if the phone is off there is no way to track it.


HTH

If your company pays for the cell phone and purchased it and issued it to the employee then it's company properly.  You need a mobile device management system to do this.  If this phone belongs to your employee, then you likely cannot legally do this without the employee's explicit permission - and if I were the employee, I'd refuse.

Google: https://www.google.com/search?q=mobile+device+management+location&ie=utf-8&oe=utf-8#q=mobile+device+management+location+tracking

Note: if this is an android phone, you can turn on location tracking - it's not real time, but you can then sign in and see a history of the location of the phone.

Is it an iPhone?

If your phone is powered off, there isn't a way to track it.  You will need to wait until it is turned on and connected to the internet.

 Follow this article from Apple.

https://support.apple.com/en-us/HT201472

 What if your iOS device is off or offline?

 And here is how you can track it.

http://trendblog.net/how-to-track-your-lost-iphone-or-ipad-without-tracking-app/

You need to make sure this is a known company policy and that you are doing this to everybody and I mean EVERYBODY.  

To do otherwise sets you and your company up for a huge discrimination and harassment lawsuit.   Not to mention it is a HUGE invasion of privacy if you track the phone outside of business hours.  No, the married guy/gal probably shouldn't be going to the local XXX bar/club, but that is not your business if it is done on their own time.

You need to talk to your HR dept.