MANSFIELD, Texas -- The family of a Rice University student who vanished during his finals said Friday they were worried about him.

The student, 20-year-old Matthew Wilson, is from Oklahoma, NBC 5 reported, but he spent Thanksgiving in Mansfield at his sister's home.

"I'm not worried about Christmas," said Wilson's mother, Cathy. "If Matthew doesn't come home, I'm not worried about Christmas."

Wilson added, "I can't sleep at night. All I can think about I'm trying to solve this in my head."

Wilson vanished Saturday, just before finals, authorities said. At first, his family said they thought he was studying, but not anymore.

Investigators said they found Wilson's cell phone in his off-campus Houston apartment. Wilson's car and backpack are also missing, police also said.

Wilson's family said he didn't drink alcohol or use drugs, and he seemed to be happy the last time they were all together for Thanksgiving in Mansfield.