Culkin and Song attended Instagram's Knott's Scary Farm celebrity night on Friday, where a source tells ET the two were very "affectionate" with one another and openly held hands.
"Parkgoers said they were very cute with each other holding hands and very affectionate," the source says. "Looked like they were having a great time."
Culkin appeared to be on a double date with his close friend, actor Seth Green, and his wife, Clare Grant, according to our source. Culkin and Song are both starring in Green‘s upcoming directorial debut, Changeland.
"They all looked super comfortable together and like they were having a great night out," the source says.
Culkin, 37, and Song, 29, clearly had fun together riding the amusement park rides, including roller coasters GhostRider and the Silver Bullet. During GhostRider, Song adorably held on to Culkin's arm.
ET has reached out to their reps for comment.
ET's Katie Krause spoke to Song on Friday at Knott's Scary Farm, where the former Disney star talked about her upcoming film with Culkin.
"It's basically about a guy who is going on a planned a trip with his wife, finds out that she's cheating on him, and his best friend jumps in last minute, and it's their adventures in Thailand and the people they sort of come across, and the crazy adventures that happen when you go on a trip across the world," Song explained. "It's been incredible. We spent five weeks in Thailand shooting this. Seth directed and wrote and starred in it, and this has been in the making for the last seven years, so he made it happen, it was incredible -- it was like, Changeland for me. That sounds super cheesy but, like, I came back like a different person."
She also talked about Green getting the notoriously private Culkin to star in his film.
"Seth and Him had done Party Monster together so they had been friends forever, so I think that's probably how he got [him] in, but it was a wonderful experience," she said. "Everyone was great ... we had the best time ever. Everyone was lovely, we just got to go to Thailand and hang out with our best friends for five weeks."
Culkin and Song first sparked dating rumors when they were snapped at celeb hot spot Craig's in Los Angeles in July. However, Song declined to comment on the romance rumors on Friday.