Pickpockets can be found in almost every city in the world - however it does seem that most of the reports seem to be focused in Europe, South America, and other parts for the world where tourists tend to visit. If one really wanted to make sure they were prepared to avoid these types of thieves - you should spend a little time to understand how they operate.
Pickpockets use many of the same scams in Paris and they do in Barcelona, as the do in Mexico City. Most of their techniques have been honed over the last 30 years and passed on from crook to crook.
Just take a little time to research how pickpockets operate so you can be alerted to their sneaky ways before it is too late.
Lastly, know that pickpockets come in all skill levels - from the opportunist - who is just starting to learn his/her trade, to the full blown professional thief who works in a team, and even used distraction as one of their ways to get you to turn your attention away from your property.