I need a function to search in all rows of a treegrid, even if its nodes are closed. I try with findCell() method but it just search in open nodes… is there a function like findCell that search the information in the whole treegrid??

Problem confirmed and fixed ( dhtmlxGrid 1.3 ) , the updated code will be available as part of next version
If you need fix ASAP just locate next code in dhtmlxGrid

      for (var j=0; j<this.rowsCol.length; j++){
         var val=z.getValue();

         if ((val||"").toString().indexOf(value)!=-1) res[res.length]=[j,i];

and replace it with

         var val=z.getValue();

         if ((val||"").toString().indexOf(value)!=-1) res[res.length]=[id,i];