How Do You Let an Employer Know An Employee is Stealing

[elc]

My question involves criminal law for the state of: CO

I have an issue with an old friend of mine. She steals regularly from work. I am talking, 1000's of dollars a month. I wouldn't be surprised if she exceeded stealing $5,000 a month. She talks of trips she will take, etc. I have heard the whole deal, how she does it, how much she takes, and how easy it is. She is welcomed back to this position every year, and every year she does the same. I worked for the company as well, in a separate department. It's a fairly small company, and they have a lot of trust in their employees. No cameras, no questions ever asked. They obviously haven't noticed anything. With this year's financial difficulties felt everywhere, it's bothering me even more, since the company announced they had lost thousands and thousands of dollars last year. She also has stolen from another small company she works for...family owned. It all just really gets to me that this can happen. I work hard for my living, as many people do. My question is:
Do you inform a company/employer that this is going on? And if so, how would you go about it?

[Mr. Knowitall]

Phone call, letter, email.... How hard is it to communicate in this modern era?