Good question! Green's style in this novel is not exactly literary; his dialogue is very modern, and much of the narration is straightforward description, given that the narrator is the very realistic seventeen-year-old Quentin.

But if we're looking for 4 different examples of a particular literary device in this novel, let's pick the simile. It's used often enough that we can find plenty of examples.

(Imagery would also work, if you prefer a different device: you can simply select any passage in which Quentin's narration emphasizes what things look like in the his habitually specific way. Hyperbole would work, too; Quentin often exaggerates his own feelings of fear and frustration. And of course, metaphors would work: both Margo and Quentin often refer to the "strings" inside humans.)

Here are some good examples of similes throughout the novel:

1. From Chapter 3: "[Margo] squeezed on [the air horn] and it let out an excruciatingly loud honk that felt in my head like the auditory equivalent of an aneurysm..."

By comparing the sound of the air horn to an aneurysm, Quentin colorfully expresses the painful volume of the sound. We get a better sense of Margo's craziness, spontaneity, and disregard for other people's comfort, thanks to this simile. 

2. From Chapter 8: "Strips of cracked paint wrinkled away from the walls, like insects clinging to a nest."

This very visual and disgusting simile helps us create a mental picture of the state of decay into which the building has fallen. Ben, Radar, and Quentin are there to search for Margo, and by understanding how nasty and decrepit the building is, we better understand the difficulty of their search.

3. From Chapter 10: "Why hadn't she left me a specific place? All these scary-as-hell clues. All this intimation of tragedy. But no place. Nothing to hold on to. Like trying to climb a mountain of gravel."

Here, the simile that Quentin imagines likens his task of finding Margo to an attempt to clamber up a pile of tiny rocks. It helps us understand his frustration as something more concrete than just a boy staring at a map of random places. We imagine trying to sink our feet into piles of gravel that give way easily, and now Quentin's frustration feels more real.

4. From Chapter 13: "But no, as he sucked on that beer spout like it was mother's milk, little trickles of beer spilled from the side of his mouth..."

This simile likens Ben's keg stand drinking to a baby who eagerly drinks milk from his mother. It reveals that Ben's behavior, though obscene and reprehensible, is also earnest and intense. The simile helps characterize Ben as someone who really engages with life and what it has to offer, even though Quentin sees the behavior as childish and meaningless.