gistfile1.js

function childFind(selector, which) {
  if (!this || !this.length) return $([]);
  
  which = (which || 'previous') + 'Sibling';
    
  var element = this[0][which];
    
  while (element && (element.nodeType !== 1 || !$(element).is(selector))) element = element[which];
    
  return $(element);
}
    
$.fn.prevFind = function(selector) { return childFind.call(this, selector); };
$.fn.nextFind = function(selector) { return childFind.call(this, selector, 'next'); };

http://jsperf.com/prevall-vs-prevfind/3