After the ending of Alan Wake and its DLC episodes, a sequel seemed necessary to wrap up the storyline. While critically praised, sales for the Xbox 360 exclusive were not as high as they could have been, so there wasn't a rush to formally announce a sequel.
Game Sector noticed a recent job post from Alan Wake's developer, Remedy, looking for a senior developers who will work on an Xbox 360 title that will have a "well-balanced mix of compelling narrative and intense action".
They also checked out the most recent Official Xbox Magazine and found the following item: "Yes or no for Alan Wake 2? We shook The Ball and it said, It looks promising". While not any kind of official confirmation of the sequel, this is confirmation that Remedy is currently working on a new game for the Xbox 360. They are known for their long development cycles, so we don't expect any kind of announcement until they are ready to show off in-game footage. It may be a little too soon, but I'm hoping we see something at this year's E3.