Police created fake identities to enter the social networking site and found what Fair Lawn High School students were going.
Officers stopped the caravan a few miles from the high school and arrested four 17-year-old boys who officers say were carrying marijuana, scales and baggies commonly used to package the drug.
School Superintendent Bruce Watson says the district doesn't check Facebook on a regular basis unless there's a reason. Watson says the district generally leaves Internet patrolling to police.
Police Sgt. Derek Bastinck says teenagers are cavalier about accepting people into their network of friends.