Since Ponyboy is the narrator, he doesn't speak of himself much in metaphor, although he uses a lot of metaphor for other characters, like comparing Johnny to "a little dark puppy." I hope that these metaphors work for you. They are not taken from the novel but made up by me to describe Ponyboy. I think that is what you are asking for.
"Ponyboy is a light in an ocean of darkness." The metaphor works to describe Ponyboy because of how much he stands out against the other Greasers. They even recognize it about him. That's why Johnny wants him to "stay gold." It's why the other Greasers worry about him turning hard. They don't want him to do that. Pony is immediately noticeable much like a light is very noticeable on dark water. Cherry even notices it about Pony.
"Cherry was looking at me. "What's a nice, smart kid like you running around with trash like that for?"
"Pony is the moral compass of the Greasers." This metaphor ties in with the previous metaphor. It's what makes Ponyboy stand out. He might be in a Gang. He might get into rumbles and fights, but he has a strong sense of right and wrong. He doesn't treat Cherry like a piece of meat the way that Dally does. He risks his own life to save the children in the church. He's always influencing the gang to consider consequences. He really is like gold. He's constant and extremely valuable to those around him.