Why was finding Alaska so important?

The novel Looking for Alaska is centered around a metaphorical search, which shifts throughout the novel. The phrase "looking for Alaska" refers to the search for identity, in many different senses of the definition.
The protagonist, Miles, begins the novel by searching for himself and seeking the "Great Perhaps" missing from his life. His world changes when he meets Alaska, whom he quickly begins falling for. It's clear from the start that Miles doesn't really understand or know Alaska; instead, he merely views her as the solution to all of his problems. In short, Miles views Alaska only in terms of how she can help him, versus seeing the full person she is.
When Alaska dies suddenly in a car crash, Miles and his friends believe there is more to the story. A mystery surrounds her death, and they have questions regarding all of the circumstances. Here, they are "looking for Alaska" in order to uncover secrets of her past to figure out what really happened on that night. These questions remain largely unanswered.
The last meaning of the phrase can be found at the end of the novel when Miles finally realizes he will likely never have answers about Alaska and the mystery of her death. He admits he never fully knew Alaska and that he will have to let go of her in order to move on. In a sense, he stops looking for Alaska, in order to finally find himself.