( CNN ) -- Nearly 100 people , including police , volunteers and family members , were searching Monday for a University of Florida student who went missing four days ago in Gainesville . Police fear Christian Aguilar could be seriously injured , disoriented and unable to seek medical attention . Aguilar , 18 , disappeared last week after an altercation over a girl , his father told CNN affiliate WCJB . According to police , Aguilar and another 18-year-old man had an altercation on Thursday . The second man told investigators he left Aguilar in the parking lot , but searchers using helicopters and scent dogs failed to turn up any trace of him , police said Sunday . Authorities have said the man is a `` person of interest '' in the case and charged the 18-year-old with depriving a victim of medical care , a third-degree felony . He underwent a psychiatric evaluation Monday after he told investigators that he wanted to kill himself and was subsequently booked in the Alachua County Jail , Officer Ben Tobias said . Police suspect foul play , Tobias said . Family members , who have plastered the area with fliers and taken to Twitter to generate leads , have invited a nonprofit search group to help look for Aguilar alongside family members and police . `` The search is ongoing . We 're going to keep searching until we find him , '' said Joe St. Cyr with Search and Rescue of Central Florida . American couple killed in St. Maarten . Search for missing climbers suspended . Body of missing Amtrak passenger found . CNN 's Joe Sutton contributed to this report .
NEW : A `` person of interest '' has been charged with depriving a victim of medical care . Search dogs help police , family members look for missing student . Christian Aguilar disappeared Thursday after a fight with another man , police say .