Learn Russian: Фанаты не могут найти спортсменов.

Because спортсмен (athlete) is a living person (an animate noun). When plural animate nouns are the direct object of an action (in the accusative case), their endings copy the genitive plural. So, instead of keeping the regular plural form, we use the genitive plural form спортсменов.

Wait, фанаты (fans) are living people too. Why doesn't that word end in -ов?

Because the fans are the ones doing the action. They are the subject of the sentence, which means they stay in the nominative case. The special animate rule where the ending changes to look like the genitive only happens when the living noun is the target of the action (the accusative case).

Why do we use могут here instead of умеют for "cannot"?

Both verbs mean "can" or "to be able to," but they are used differently. Уметь is for learned skills, like knowing how to swim or speak a language. Мочь is for physical ability or possibility in a specific situation. The fans haven't forgotten how to find people; it is just physically impossible for them to locate the athletes right now.

Could I use искать (to look for) here instead of найти (to find)?