Orcs would be a likely kidnapper. They have a long - standing enmity with the elves, and Legolas being an important elf, would be a valuable captive. They could either want to torture him for information or use him as a bargaining chip with the elves.
A group of humans who are jealous of the elves' long life and magic could also be the kidnappers. They might believe that by kidnapping Legolas, they can unlock the secrets of elven immortality and magic for themselves.
It could be an orc warband. Orcs have always been enemies of the elves, and they might see Legolas as a valuable captive either for ransom or to torture. Another possibility is a rogue wizard. Wizards who have turned to the dark side often seek powerful beings to experiment on, and Legolas, with his elven magic and skills, would be an interesting subject.
It could be an obsessed fan. You know, someone who has taken their admiration too far. They might think that by kidnapping Liv and Maddie, they can have them all to themselves and be part of their exclusive world. This type of kidnapper would be really unpredictable as they are acting out of an extreme and abnormal form of love.
It could also be a secret organization within the Naruto universe that we don't know much about in the original story. This organization might be aware of some hidden prophecy or potential in Naruto related to the Nine - Tailed Fox. They kidnap him with the intention of either preventing that potential from being realized (if they see it as a threat) or using it for their own mysterious ends.
It could be someone Reid put away in the past. Maybe a criminal who has held a grudge against him ever since and has now found an opportunity to kidnap him for revenge.
It could be a jealous rival. Maybe someone who is envious of Felicity's intelligence or her relationships. Without her glasses, this person might think she's more vulnerable and easier to manipulate or hold hostage to get what they want.
Maybe it's a rogue wizard. Wizards can be unpredictable, and one with a grudge against the elves or a thirst for power might kidnap Legolas. He could think that Legolas has some sort of magical essence that he can use for his own dark magic experiments.
It could be a jealous coworker. Maybe they feel that Kaoru is getting all the attention or a promotion they wanted. Another possibility is a patient who has become obsessed with Kaoru during their treatment. Or perhaps it's someone from Kaoru's past who has a grudge against her.
The Black Hood is a likely candidate. Since he has a history of causing trouble in Riverdale, he might kidnap someone to send a message or continue his reign of terror. He could target Cheryl, for example, thinking she's a symbol of the wealthy and corrupt in the town.
Maybe it's a group of villains working together. They could be from different factions but united by the idea that Izuku has the potential to become a huge threat to their plans. They might kidnap him to either eliminate him or turn him to their side. Also, it could be a lone, obsessed fan of a villain who wants to prove themselves by bringing Izuku to their idol.
A group of outcasts from different islands might kidnap Moana. They feel that they have been wronged by the 'normal' society that Moana represents. They hope that by kidnapping her, they can get the attention they deserve and force the islands to change their ways. But Moana listens to their grievances and tries to find a way to help them while also finding a way home.