Why does the narrator seek out Simon Wheeler in "The Celebrated Jumping Frog of Calaveras County?

The narrator seeks out Simon Wheeler because the narrator's friend back East requested that the narrator find Simon and ask him about another guy, named Leonidas W. Smiley.

Presumably because the narrator is a good friend, he does what is asked of him, and looks for Simon so that he can ask about Leonidas and, hopefully, contact his friend back East to let him know that Leonidas is okay.

Of course, that's not exactly what...

The narrator seeks out Simon Wheeler because the narrator's friend back East requested that the narrator find Simon and ask him about another guy, named Leonidas W. Smiley.

Presumably because the narrator is a good friend, he does what is asked of him, and looks for Simon so that he can ask about Leonidas and, hopefully, contact his friend back East to let him know that Leonidas is okay.

Of course, that's not exactly what happens in the story, though! The narrator does find Simon Wheeler, and he does ask him about Leonidas W. Smiley, but the narrator realizes just as we the readers do that his friend has played a joke on him. There is no such person as Leonidas W. Smiley, and his name, "Smiley," only reminds Simon about a long, boring story about a different guy with the same last name ("Jim Smiley") and Simon proceeds to tell this entire story to the narrator. The narrator is really annoyed and realizes that his friend probably planned out the whole interaction as a practical joke.

All this is reported within the very first paragraph of the story. It might be a little hard to understand, since it involves so many different men, so I'll also explain it like this. Here are the events in the order they happened, even though the narrator explains them all at once:

1. The narrator's friend asked the narrator to ask Simon Wheeler about Leonidas W. Smiley.

2. The narrator finds Simon and asks him about Leonidas.

3. Simon has idea who Leonidas is.

4. Leonidas's last name, "Smiley," reminds Simon of another guy, Jim Smiley.

5. Simon tells a long, silly, boring story about Jim Smiley to the narrator.

6. The narrator realizes his friend has tricked him by sending him on this errand--his friend probably knew Simon well and knew what would happen if someone mentioned the name "Smiley" to him.