OK I'm not 100% on Mac but here are a few things that come to mind. First you should have already installed some form of HTC Sync on your Mac desktop/laptop to get the drivers for the phone. Second if you are sure the drivers are there the next step is to have the phone unlocked and displaying your home screen while plugged in. If the phone isn't displaying the home screen it locks its self as a security thing to prevent someone from accessing your data simply by having the phone. The HTC One doesn't offer a charge only or drive only option as phones have in the past however it does offer an option to piggyback on your internet connection if plugged in to a system that has internet. There are 3 options and I'm not sure if one of these settings could stop you from seeing your drive, but you can look at them if the first two suggestions don't give you what you want. In Settings>More (under your data options)>Mobile network sharing>USB network setting the options are None - Smart network sharing - Mobile Broadband Connect - Internet pass-through. You can read the descriptions and see which fits you best, however I will say that I have Smart network sharing selected and I am, with the previous two suggestions, able to see my device as a dive under My Computer. Again not sure how that translates to Mac, but my feeling is that where ever you are able to see your drives i.e. hard drive, disc drive, memory sticks ect. you should be able to see your device.
One last thing if you have the drivers, have the phone awake and displaying your home screen, and your settings are good and still are unable to see your device you may need a different USB cable. Micro USB cables do go bad. They usually loose the ability to charge but can loose the ability to transfer data while continuing to charge.