I am currently helping someone find their End Portal on their world with the latest updates on the 360 console. We used the Eye of Ender and it did lead us to a big stronghold with a big library, some stairways, silverfish blocks and a bunch of hallways. We consulted YouTube and the videos we watched confirmed what we should be looking for but we still haven't found the portal. Any suggestions?
What you can do is go above ground, and then get a little height (climb a tree or nerd-pole up a bit), then throw a few Eyes of ender. The point where it touches the ground should be directly above the portal room.
However, if you are still in the fortress, it is best to stay on one level (as best you can) while following the Eyes. When they float down tho the floor, the portal is beneath you. It will be hard to determine if the portal is above you because a) I believe that the portal spawns on the lower levels of the dungeon anyway, and b) there is a low ceiling, so the Eyes will always be hitting the ceiling.
However, if the eyes gravitate to the same spot, it (should) be above you.
You could also try the "X-ray vision glitch" to attempt to see the portal: Set up a redstone circuit that will use a piston to push a block of tnt onto your head. If done right, you shouldn't get any suffocation damage.
Make sure the redstone doesn't connect to the TNT!
Alternatively, depending on when the world was made (specifically if it was made prior to 'The End' update), it is possible the portal has never even spawned, and the Eyes are only showing where it should be, even though it's not. If that is the case, create a new world with the same seed. The portal will spawn in that world. NOTE: this is only possible if you know the original seed.