The jets were armed but did not open fire, North American Aerospace Defense Command spokesman Cameron Hillier said by phone.
Sea-Tac operations have resumed as normal, airport officials said; flights had been grounded during the incident.
Questions have been raised about how a plane can be stolen from a busy airport. They took care to point out that the crash was not an act of terrorism.
He was believed to have been killed in the crash. Southers is director of homegrown violent extremism studies at the University of Southern California.
One user tweeted, "Some dude stole a plane from #Seatac (Allegedly), did a loop-the-loop, nearly crashed into #ChambersBay, then crossed in front of our party, chased by fighter jets and subsequently crashed".
Video showed the 76-seat aircraft doing large loops and other risky maneuvers as the sun was setting.
It is unclear how the employee was able to taxi the plane on a runway and take off without authorisation.
The man - addressed as "Rich" - said he was concerned he was going to run low on fuel.
All flights were grounded at Seattle-Tacoma global airport in the USA when a passenger plane took off without permission.
On Saturday morning, White House Press Secretary Sarah Sanders told media that President Donald Trump was briefed on the incident and is now "monitoring the situation" in Seattle. He's now at his New Jersey golf club. She commended the response effort for its "swift action" and public safety protection. His identity and condition are unknown.
Horizon Air chief operating officer Constance von Muehlen issued a video statement describing the incident. Ground service agents' job duties are to load and unload bags, direct aircraft for takeoff and de-ice planes in the winter.
"An airline employee conducted an unauthorized takeoff without passengers at Sea-Tac; aircraft has crashed in south Puget Sound", it read. Troyer said F-15 aircraft were in the air "within a few minutes" and the pilots kept "people on the ground safe". He said he thought it was some military drills from the nearby Joint Base Lewis-McChord.
"Even just ground people working on the planes, they have access to inside the planes on ramp", Stratman said.
The sheriff said earlier that the man was a airline mechanic, but the airline said the employee was a ground service agent.
Unverified video footage on social media showed a large plane flying above the Seattle area with an F-15 following it. There were no passengers aboard. "No others involved", the office of the Pierce County Sheriff said.
Alaska Airlines planes are seen at Seattle-Tacoma International Airport in SeaTac, Wash., Oct. 30, 2013. There were reportedly no passengers on the plane.
The married airport employee, 29, "hijacked" the Alaska Airlines plane before performing stunts in the sky as he was tailed by fighter jets today.
No other information was immediately available.
Alaska Air Group CEO Brad Tilden said at a news conference Saturday in Seattle that the man, identified by sources familiar with the investigation as Richard Russell, was "fully credentialed" and authorized to be working near the aircraft.