A “cowardly” driver in Methuen hit an 11-year-old girl and drove off last night, leaving her with life-threatening injuries, according to police, who launched a massive search for the suspect.The incident occurred about 9:45 p.m. when the child was crossing Broadway near Kirk Street with her parent, police said in a statement.The vehicle went through “the intersection at a very high rate of speed, struck her,” police said.The driver then fled down Broadway toward Lawrence, cops said.