If a pilot that has problems with alcohol asks for help, they will be entered into a program to help him. He won't be flying during this time. He also has to work on getting his medical back (proof of sobriety, etc.. whatever the FAA does, I'm not sure). He won't, however, be jailed or fired if he didn't do anything illegal.
There is absolutely no recourse for turning a fellow FAA-regulated employee in for alcohol abuse. Now, the proper way to do it is get the person in question to call out sick or otherwise not attempt to go to work and then get them into the above program. It's the last chance to save his career (and possibly his marriage, or even life) because once you show up at the airport, the intent to fly is there and it will not end well if caught.
"Either you're calling out sick or I am and when they ask why I called out sick I'll tell the truth" will usually get the proper response from someone.