With less than a month until Star Wars: The Force Awakens grips the entire world, it's not even worth it to ask why we haven't seen a single glimpse of Luke Skywalker. What would be the point? J.J. Abrams and Lucasfilm have held on to the secret this long, and nothing is going to break that. Especially not Mark Hamill, who talked to PC Gamer about his ability to keep the secret, reminding them that he's kind of been through this stuff before...
"I have something coming out where there's an amount of money that if it leaks because of me, I don't get that payment. If I keep it a secret until the day it comes out, I get that payment....I'm good about keeping secrets. I'm proud of the fact that I knew a year and a half before anybody else that he was actually dad-Vader. I didn't even tell Harrison, or my wife, because I thought it would be terrible if she said "you know what" to a fan and it got out, because [Empire Strikes Back director] Irvin Kershner said 'I know something, I'm going to tell you. George [Lucas] knows, I know and now I'm gonna tell you, and if it leaks, we'll know it's you', because the line originally was 'you don't know the truth, Obi Wan killed your father' and he said 'we're going to take that line out and put in 'I am your father'."
So just don't even bother, okay? And if you're looking for something, ANYTHING new on the film, take a gander at the latest image of the evil, Darth Vader-obsessed Kylo Ren (Adam Driver), courtesy of Empire.