Photos published by the Daily Mail on Monday show a healthier-looking Culkin in Paris. The trio visited chef Joel Robuchon's L'Atelier, a restaurant with two Michelin stars.
After eating, the three walked along the Seine on the Pont des Arts. Fellow actor Seth Green and Green's wife Clare Grant joined them later.
The photos also show the 19-year-old Paris and the 37-year-old Culkin smoking together. The friends got matching tattoos over the summer.
Photos previously published by Entertainment Tonight show Song and Culkin after a shopping spree at the Monoprix store. Culkin carried several full bags, while Song was carrying a teddy bear.
"Parkgoers said they were very cute with each other holding hands and very affectionate," a source told ET. "Looked like they were having a great time."
The 29-year-old Song also posted a photo from the Paris trip on her Instagram page.
Culkin and Song were first seen together in July. The two are also going to appear in Green's film Changeland.
"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 told ET about the new movie.
"It's been incredible. We spent five weeks in Thailand shooting this," the former Disney Channel star continued. "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."
In 2012, Culkin faced tabloid rumors of drug abuse and illness after photos of him looking gaunt were published, but photos of the former Home Alone star this year show him looking much healthier. He also cut his long hair after he started dating Song.