http://mattbramer.blogspot.com/2014/01/fire-workflows-with-initiation.html

Fire Workflow with Initiation Parameters

// Example itemUrl for Document:
// http://<site>/<DocLib>/doc7.docx

// Example itemUrl for Item:
// http://<site>/<customsite>/Lists/<ListName>/<ID>_.000

function fireWorkflow ( itemUrl, workflowName, workflowParams ) {
	workflowParams = workflowParams || "<root />";

	$().SPServices({
		operation: "GetTemplatesForItem",
		item: itemUrl,
		completefunc: function ( data, status ) {
			var workflowGUID = ""

			;

			$(data.responseXML).find("WorkflowTemplates > WorkflowTemplate").each(function(i,e) {
				var $this = $( this )

				;
				// hard coded workflow name
				if ( $this.attr("Name") === workflowName ) {
					var guid = $this.find("WorkflowTemplateIdSet").attr("TemplateId");

					if ( guid ) {
						workflowGUID = "{" + guid + "}";
					}

					// Stops #each iteration
					return false;
				}
			});

			$().SPServices({
				operation: "StartWorkflow",
				item: itemUrl,
				templateId: workflowGUID,
				workflowParameters: workflowParams,
				completefunc: function( data, status ) {
				// Continue processing after workflow is fired.
				}
			});
		}
	});
}

fireWorkflow( "http://<site>/Lists/<listName>/<ID>_.000", "Workflow Name", "<Data><TestField>All up in your SharePoints.</TestField></Data>" );