window.addEventListener('load', function() { 

  var b = document.getElementById('box'),  
      xbox = b.offsetWidth  / 2, // half the box width 
      ybox = b.offsetHeight / 2, // half the box height  
      bstyle = b.style; // cached access to the style object  

  b.addEventListener('touchmove', function(event) {  
    event.preventDefault(); // the default behaviour is scrolling    
    bstyle.left =  event.targetTouches[0].pageX - xbox + 'px';   
    bstyle.top  =  event.targetTouches[0].pageY - ybox + 'px';  
  }, false);  

}, false);