Four weeks into a living nightmare, the parents of missing Westchester student Lauren Spierer yesterday pleaded with the parents of her Indiana University friends to stop stonewalling cops.

“We are appealing to the parents of the children who may have first hand or second hand knowledge of what happened to Lauren,” Lauren’s dad, Robert, said at a Friday press conference.

“Help your children find the courage to come forward,” he said, tears flowing. “Help them find their moral compass to do the right thing.”

Investigators believe Lauren’s friends know more than they’re telling about what happened in the hours before she disappeared June 3, after a night of partying.

Lauren’s mom, Charlene, has said only one of Lauren’s friends has voluntarily come forward with information.