chelsea ellen bruck , 22 , was last seen in the early hours of october 26 in frenchtown township , michigan dressed as the batman villain poison ivy .
police searched an area near a ford motor company plant in michigan .
the sheriff 's office declined to discuss media reports that part of chelsea 's costume were found .
she was last seen in the parking lot with dark-haired man at 3 am .
the party had to be shut down after numbers swelled from 500 to 800 people .