The above answer gives most of the similes, but there are a few more, and one of them is arguably the most significant simile in the story.

Blackie realized he had raised his hand like any ordinary member of the gang.

In this context, Blackie, who is the leader of the gang, is acting orderly, not taking charge. This action is uncharacteristic for him. To make this point, Greene says that he is acting like a typical member. The presupposition is that Blackie does not usually raise his hand.

Two were missing—Mike and another boy, whose parents were off to Southend and Brighton in spite of the slow warm drops that had begun to fall and the rumble of thunder in the estuary like the first guns of the old blitz.

In this context, the destruction of the house has begun. To make this point, the destruction is likened to the “first guns of the old blitz.” The blitz, of course, is a reference to the German tactic of bombarding with heavy artillery a region. By bringing this idea into the destruction of the house, the devastation of the Germans is introduced. More significantly, the idea of a systematic destruction is introduced.

One moment the house had stood there with such dignity between the bomb sites like a man in a top hat, and then, bang, crash, there wasn’t anything left—not anything.

This quote is probably the most memorable sentence in the short story. The boys destroyed one of the few buildings that was not hit in the German air raids. Moreover, the house was not an ordinary house; it was dignified and proper. Also, the idea of the top hat brings the connotation of wealth and high society into view. Its destruction is, therefore, all the more significant. Destruction does not show favoritism.

Similes definitely add to the artistry of "The Destructors"  by Graham Greene.  He uses them to help describe the scenes in the story and to characterize the boys.

Simile #1: "A smaller bomb and some incendiaries had fallen beyond, so that the house stuck up like a jagged tooth..."

This simile is describing the site of the bombings in London during WWII. The neighborhood the boys live in has been ravaged.  One remaining home has survived the destruction, and describing it like a jagged tooth implies the devouring of the area, ugliness and pain.

Simile #2: “It’s got a staircase two hundred years old like a corkscrew. Nothing holds it up.”

Trevor knows about suspended staircases because his father is an architect, but he needs to describe it in terms the boys can understand.

Simile #3: “We’d be like worms, don’t you see, in an apple."

Here Trevor is describing the destruction they will do on the house. Worms are on the inside of an apple, not visible on the outside. Likewise, the boys will destroy the house from the inside with no visible damage on the exterior.

Simile #4: "The loo stood like a tomb in a neglected graveyard."

This simile speaks to the destruction of the area.  The outhouse is small in the midst of the rubble.  The comparison to a tomb gives it the image of death, which the war has caused.