themer is not currently available on the playstore m8,as for crashing remember it is still beta,some have had issues while others haven't.I am also not fully sure it is cm11 compatable not having used it.If it was working before then it is possible it is the rom.Have you tried totally removing themer including the mycolorscreen folder,then re installing ?
The Lord of the Blings
One theme to rule them,one theme to find them
One theme to bring them all,and in the darkness bind them.
Over one hundred themes added to themer app