Mercedes are not stolen much, this is because high end cars are hard to shift and relatively less in demand,
the cars that get stolen the most are smaller cars like Mehrans, cuores and Alto's etc,
reason being that these cars are in high demand so they're easy to shift, and the theives do not have to retain the possession of a "hot" (stolen) vehicle for longer than necessary,
also it is easy for them to clone the vehicle on to the identity of a totalled one as the identity is easily and widely available,
as someone mentioned, during election time, a significant number of 4X4s are stolen however these cars are not commonly stolen, reason being that they are normally owned by connected people, theives, smugglers and politicians etc,
so they tend not to steal each others cars and also it gets hard for them to get the Police to go to sleep on such cases.
Those few 4X4s or high end cars which do get stolen end up in FATA, NWFP, Baluchistan or in the hands of people who do not require number plates nor do they get stopped by virtue of their contacts, resources or jobs.