During a trip to New York, Lucy Clode, 17, from Dollar, Clackmannanshire, took pictures of Franco when he emerged from a Broadway theatre and posted them on the photo-sharing app Instagram.
They then struck up an online conversation with the 35-year-old actor asking the teenager her age, if she had a boyfriend and where she was staying.
On the morning talk show Live With Kelly and Michael in New York, Franco said that he used "bad judgment" and had "learned my lesson".
He said: "It's the way that people meet each other today, but what I've learned, I guess because I'm new to it, is you don't know who's on the other end.
"When you meet in person you get a feel for them, you don't know who you're talking to.
"I used bad judgment and I learned my lesson.
"Unfortunately in my position, not only do I have to go through the embarrassing rituals of meeting someone, but if I do that, then it gets published for the world so it's doubly embarrassing."
Ms Clode was said to be in New York with her mother for an 18th birthday present.
She told a friend on Instagram: "James Franco asked me to meet him! It was really him and I rejected him!"