Authorities in Indiana have activated a Silver Alert for a missing teenager who disappeared last week.

Robert “RJ” Williams Jr., 16, was last sighted on December 17 in Indianapolis, as reported by WISH. The day after he went missing, Indianapolis police found his gym bag and backpack abandoned on a dock near the White River.

Williams is on the autism spectrum and has a mild intellectual disability, according to information from the Indianapolis Star. His cognitive abilities are similar to those of a 10- or 11-year-old, and he has been diagnosed with psychosis and disruptive mood dysregulation disorder.

The teenager was reported missing after he did not return home from Purdue Polytechnic High School. It is suspected he visited a McDonald’s restaurant prior to his disappearance.

Williams is described as 5 feet 9 inches tall, weighing 185 pounds, with black hair and brown eyes. At the time he was last seen, he was wearing a gray coat, blue sweat pants, and black tennis shoes.

Anyone with information regarding Williams’ whereabouts should call the Indianapolis Metropolitan Police Department at 317-327-6541 or call 911.