A cal State Northridge student from Saudi Arabia who disappeared in Riverside County last month remains missing, and the FBI is now assisting in the investigation, authorities said on Friday. Abdullah Abdullatif Alkadi, 23, an electrical engineering student, was last seen Sept. 18 at his home in the 9900 block of Reseda Boulevard, according to the Los Angeles Police Department. The FBI is "assisting with resources" in the search for Alkadi, which is being led by the LAPD, said FBI spokeswoman Laura Eimiller. The student's older brother, Ahmed Alkadi, said his sibling sold his car on Sept. 17. Police have since found the car, an Audi, which was sold on Craigslist, CBS LA-TV and the Associated Press reported. The buyer is not believed to be linked to Abdullah Alkadi's disappearance, CBS LA reported. Abdullah Abdullatif Alkadi is pictured in this undated handout photo provided by the Los Angeles Police Department. REUTERS/Los Angeles Police Department/Handout The missing man's cellphone was traced to Beaumont, a city in northwestern Riverside County, but was then deactivated. Ahmed Alkadi said he knew of no ties to his brother in that area. CSUN President Dianne F. Harrison said in a statement last week addressed to the "CSUN community" that school officials "have been in touch with Mr. Alkadi's family to express our support during this difficult time." "While there is little information at this time regarding what occurred, the university is concerned with the circumstances of his disappearance," Harrison said. On his Twitter account, Abdullah Alkadi describes himself as "an ambitious guy who's looking to make a difference in the future." His most recent tweet, on Sept. 14, is written in Arabic: "God, make me happy for more pain than I have suffered. Relieve me for more than I have been tired. Do not disappoint my hopes. You are my fortitude." On June 23, he wrote: "To Saudia Arabia wish me a safe trip." He wrote a month later that he was "back in Los Angeles." Police described Abdullah Alkadi as being 5 feet 3 inches tall and about 110 pounds, with black hair and brown eyes. He was last seen wearing a blue shirt, blue jeans and beige shorts. Anyone with information regarding his whereabouts was urged to call the LAPD's Missing Persons Unit at (213) 996-1800.