Person or Group field add value current user CSOM

Hello.  I want to update a multiple person field. This my code:

ExecuteOrDelayUntilScriptLoaded(updateUserField, "sp.js");
function updateUserField(){
  var itemId = 1;
	var ctx = new SP.ClientContext.get_current();
	var list = ctx.get_web().get_lists().getByTitle('Calendar');
	var item = list.getItemById(itemId);

  var newUser = new SP.FieldUserValue();
  var userid = _spPageContextInfo.userId;
  newUser.set_lookupId(userid);

	item.set_item("ParticipantsPicker", userid);
	item.update();
	ctx.executeQueryAsync(
		function() {
			console.log('Update');
		},
		function(sender,args) {
			console.log('An error occurred:' + args.get_message());
		}
	);
}