His fans call themselves Gyllenhaalics and there is no intervention. They just need to have their fix of those pecs and that sweet smile.

In Chicago, they gathered early in the morning at Millennium Park. Their ages ranged from 5 to 65, and they were on a mission to find the object of their addiction: Jake Gyllenhaal.

The 30-year-old heartthrob was filming a scene for his new movie “Source Code” in the park, and pandemonium ensued.

“Chicago is so cool in my book,” Gyllenhaal said. “We shot in the early morning hours and we had the whole park, but without giving too much away, we were filming in front of a statue that was very reflective. You could see the faces of the fans in the background going nuts and waving. It didn’t exactly fit into the plot about a guy who is hiding out.

“So I asked the ladies to shift a little to the left. It was pretty funny because the crowd moved together like one big dance step. It was everybody to the left in a few big steps. Then everybody to the right. I love my fans. They were so cooperative.”

In “Source Code,” opening Friday, Gyllenhaal plays Colter Stevens in an action thriller revolving around a soldier who finds himself stuck in an odd time-traveling pod that transports him into the body of a Chicago teacher stuck on a commuter train that has been bombed into oblivion. Colter winds the clock back eight minutes and is on a mission to find the terrorist before another bomb is unleashed in Chicago.

Each time he goes back for the eight minutes, he learns something new.

“Variation was key,” he said. “It was the only way this movie could be interesting. We figured out how to use this repetition to our advantage or we would be destroyed by it.”

He said the roughest part of the journey were the moments of disorientation when he travels from real life back into this unknown realm and lands in a pod.

“I knew it had to look disorientating, so what I would do is hold my breath and do a number of kung fu combinations to get dripping wet with sweat. Then we’d roll,” he recalled. “We’d do a seven-minute take and then I’d do my breath-holding routine all over again.”

He admitted that he almost passed out a few times. “The room was literally spinning, but that was great because my confusion looked so real onscreen.”

Gyllenhaal, whose most recent film was the love story “Love & Other Drugs,” said the idea of a thriller appealed to him.

“I loved that it was a film filled with twists and turns. In most films, the audience is way ahead of the story. This was unique in that it leaves you guessing,” he said. “The script gets there before the audience does.”

Director Duncan Jones said Gyllenhaal was the only man for the role.

“I’m a huge fan of Jake Gyllenhaal,” Jones said. “He’s an incredibly talented actor and he’s not painful on the eyes. He’s also incredibly brave. He’s an actor who is always willing to take a risk.”

Born to be an actor

Gyllenhaal grew up in Los Angeles with show business in his blood. He is the younger brother of actress Maggie Gyllenhaal and son of director Stephen Gyllenhaal and producer/screenwriter Naomi Foner.

“I was brought up in a family that desperately wanted to tell stories,” he said. “It was almost like a traveling circus. This is what still gives us joy. This is what matters to us.”

Gyllenhaal made his big-screen debut playing Billy Crystal’s son Danny in 1991’s “City Slickers.”

“It was crazy to be a kid on a major movie set,” he said. “I couldn’t believe that I was that close to Billy Crystal. To this day, I remember the wardrobe I wore, being in the makeup trailer and working with that cow that played Norman.”

He was a giving co-star.

“Remember the last scene at the airport with the family in the van with our new pet?” he asks. “The cow was peeing all over me.”

After that warm welcome to the biz, he went on to do roles in all kinds of films, from the small and independent (“Donnie Darko,” “The Good Girl”) and big blockbusters (“The Day After Tomorrow”). He became an international sensation playing a gay cowboy in Ang Lee’s “Brokeback Mountain.” His memories of working with co-star Heath Ledger are precious to him.

“I remember seeing him after we were both cast. We were at this party and we didn’t have real space to talk. But somehow we found a little corner and we started doing some of the lines,” he said. “We both thought the story was so beautiful and we wanted to service that story in whatever way possible.

“We had no time to waste.”

Gyllenhaal said his next film is “a beautiful screenplay about two Los Angeles police department officers. It’s about the nature of duty and friendship, and about the reasons why young guys put their lives in danger.”

No escaping the spotlight

Gyllenhaal’s only danger is the stalking paparazzi. He has had high-profile relationships with Kirsten Dunst, Reese Witherspoon and Taylor Swift.

“It would be great to just play characters and lose yourself in them while the audience loses themselves in the characters you play,” he said. “I’d much rather they know less about me and more about the characters.

“I don’t like having my life played out in the media. I’d much rather keep my private life private. At the same time, I completely understand the interest in an actor’s personal life. I am very forgiving of little 9-year-old girls who run up and say, ‘I want to marry you.’”

Gyllenhaal’s young fan club also includes his 4-year-old niece Ramona Sarsgaard, the daughter of his sister Maggie and actor Peter Sarsgaard.

“Family is the most important thing to me. I love being with my niece,” Gyllenhaal said. “Since my niece came into my life, I have a new perspective on spending time around the dinner table with the people who are special.”

They won’t have to deal with his movie star attitude, because there is none.

“If I developed an attitude, my mom would give me a real good whupping.”