Barcelona has a huge problem with this. It is damaging their image as a tourist city break.
I have probably posted on this thread before, but...
When I sketch in the street I see everything. Everything! I know every secret police, every methadone user and every street thief. A few times myself and my roller-blading mate Suzi held theives until police arrived. Within Two hours they were straight back on the street doing the same. I have loads of run-ins with bag snatchers and the like. They expect me to do nothing because they promise they won't touch my stuff - just the tourists things. I can't sit there and watch them rob people and spoil holidays people have saved up for for a year to enjoy.
Problem is the law in Spain. If you are under 18 and the goods stolen have a value of less than €600 then there is no charge. It is mostly Moroccan kids who think it is allowed, because there is no charge. Seriously, they believe this. They think if they just target rich tourists it is OK.
Huge problem for Barcelona. They need to deal with it.