Use the .getItem(value) method.
https://github.com/brianreavis/selectize.js/blob/master/docs/api.md#methods_options
Try here: http://jsfiddle.net/pzekurvp/5/
var selectizedElement, $selectizedElement;
$selectizedElement = $('#select-state').selectize({
onItemAdd: function (value, $item) {
alert(this.getItem(value)[0].innerHTML);
}
});
selectizedElement = $selectizedElement[0].selectize;