Never been there but I understand from my travels to Switzerland and Italy that many of these gangs of youth in Europe are Gypsy (seriously, there was a large group living in a field just outside Biel the last time I was there) and over watched by older members who will step in and get violent if one of the pick pockets is confronted / cornered.
You do have a lot of those gypsy gangs. I know exactly what you mean. Often times, they will employ a person begging for cash by holding a note with a picture, the note saying something like, "My father needs an operation, etc." If you give money, an overseer will see where you return you wallet and the beggar will gauge how much you have in your wallet. Some of these are beggars working alone or in small groups but some are also working with pickpocketers.
You also have the one or two person drug adicts looking to score for their next fix. You never know who is going to be on the prowl.