This discussion may contain spoilers!
Where the heck is Luke? Edit: 2nd Play-through, update is in italics
Luke conspicuously likes killing zombies
Before the party gets to the lodge, when ambushing the two zombies just before the bridge with Luke, Clementine says 'I don't know about this...' Then Luke comments that 'well it seems a bit of fun'. Clementine scrunches her eyebrows and says 'A bit of fun? Are you kidding me?' He was joking however it seemed...
Kenny seems different
When setting up the Christmas tree, Satira asks if Kenny seemed different now compared to back then. Later on, at the dinner table Kenny giggles a little too much at certain scenes (Specifically talking about the can of beans and what it does on the way out). In front of the fire for Clementine & Kenny's heart-to-heart, another joke he said to Clementine, 'WE ARE IN A DREAM'. He did say he was joking however strange his odd joke seemed. Then there was when Satira was carrying a box, Kenny came over to help. Satira said she was fine. Kenny took the box angrily anyway. Kenny called Clementine 'Duck' accidentally and might have been joking, 'Nick and Luke. Sounds like a nice match!'
Luke is screaming outside
After when William Carver storms the lodge, Clem is able to sneak upstairs with Alvin and Rebbecca. You either have the option to go downstairs to supplant Carver and help Carlos by turning in OR sneak outside, look for Luke and Kenny.
If you choose to find Luke/Kenny, after you sneak outside to attempt a re-group, first you see a doorway. If Clementine peers into the doorway, you see and hear Carlos' muffled writhing from pain. When you bend the corner, you see Kenny with a rifle pointed to the lodge. While creeping underneath the windows, you hear the muffled conversations inside. Then nearer to Kenny, you can hear wild screaming somewhere close outside. It was clearly a man's screaming.
The man's screaming sounds LOUD and un-muffled. The yell is located outside. The only males outside are Kenny and Luke. Since Kenny is in plain sight pointing his rifle when we still kept hearing screams... it is Luke.
Kenny is hiding something
Kenny was the last person with Luke after previously suggesting they fix the transformer together. (Despite Satira's request to give a hand, Kenny says it is 'Too dangerous').*
After, Clementine asks Kenny where is Luke, he dodges the question and just shoots Johnny (Carver's man). Some said they were able to get out something like, 'He was complaining about something so I told him to go take a hike'. This leads some to suspect Kenny is involved in Luke's disappearance.
That was Carlos, right?
One assumption was the man screaming is Carlos since his fingers were snapped by Carver. But the first person that popped into my mind was Luke... why did I wonder 'That sounds like Luke, is he in trouble'?
On second play-through, I am 99% confident Luke was the one yelling outside!
Suppose Kenny did something to Luke? What happened?
- Abandoned Luke unintentionally. Kenny & Luke are attacked by zombies. Kenny felt no allegiance to help and saved himself.
- Abandoned Luke with intent. Kenny has psychological issues or heard Luke say something which revealed a darkness of Luke. Else, Kenny is jealous of Luke.
Just what did Kenny do to Luke?