The part that you are interested in contains two pronouns: "ihn" and "er". Both are male, the first one is accusative, the second one nominative. Let us see what they can refer to. Before, two male nouns are introduced,
der ehrliche Finder
Now let's try to figure out what the "ihn" and "er" may refer to.
es liest ihn jemand
Here, "ihn" is accusative, it refers to what is being read not what does the reading. Now usually blog entries are read, people read, so "ihn" likely refers to "der Blogeintrag".
..., dem er die Geschichte erzählt hat.
Here, "er" does the telling, so it is likely "der ehrliche Finder". Let's replace the pronouns and see whether the sentence makes sense.
Vielleicht liest [der ehrliche Finder] ja diesen Blogeintrag oder es liest [den Blogeintrag] jemand, dem [der ehrliche Finder] die Geschichte erzählt hat:
That makes sense, in English it would be.
Maybe the honest finder reads this blog entry, or someone whom the honest finder has told the story reads the blog entry.
Or with pronouns as in the original
Maybe he reads it, or someone whom he has told the story reads it.
Of course, in English a blog entry (short blog nowadays, I suppose) is "it" not "he" or "him".