I know this is a bit old but I find the same problem, the ability does not work, so if someone can give me a solution.
Disclaimer: Based on personal experience, and there isn't much. My Rogue at lvl 64 has a PP skill of 89.
Ok, first, bind yourself somewhere safe. Rogue guild is a good option (learn the sewers if you're in Newport) but otherwise anywhere without guards is a good call as mentioned above.
Stand behind your target. (I skilled up on Green. I don't have comment on whether this is necessary.)
Use the
Sneak skill. You will get an emote for fail or success. Pay attention to this - you need a success to proceed.
Fail: You are as quiet as a herd of running elephants.
Success: You are as quiet as a cat stalking its pray.
Use the
Pick Pocket skill.
Success will either get you an item OR a message that your target doesn't have anything to steal.
Fail and you will generate heat (if you are in town.) Once you've failed, you can't try to pickpocket that same target again for a while.
Worth checking out items to provide +Skill to Sneak and Pick Pocket while you're skilling them. You can get low level versions by doing quests (appropriate for level 1 - 5) in Greater Faydark, the North Newport guild quests (super suggested!!), or as random drops from cecuvian's in Warpstone (which most people don't like doing, but you can also get a variety of quest items off of these dudes, so worth considering!)