A serial killer who has a particular interest in Reid might be the kidnapper. This could be because Reid's intelligence makes him an interesting target for the killer. The killer might want to play some sort of sick game with Reid, testing his mental abilities while he is held captive.
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 deranged fan of one of Reid's academic works. This person might have misinterpreted Reid's theories and decided that Reid was some sort of false prophet. So, in his twisted mind, he kidnaps Reid to 'correct' him.
One possible motive could be revenge. Maybe Reid has put away a relative or someone close to the kidnapper in the past. Another motive might be related to Reid's intelligence. The kidnapper could want to use his brainpower for some illegal or self - serving scheme, like cracking a code or coming up with a complex plan.
It could be a disgruntled former crew member. Maybe they were fired from the show and in their anger, they read a lot of fanfiction for inspiration on how to get back at the team. So they plan and execute the kidnapping.
One great Reid kidnapped fanfiction is 'The Abduction of Reid' on FanFiction.net. It has an interesting plot where Reid is kidnapped by an unsub with a personal vendetta. The author does a great job of building suspense and keeping the characters in - character.
Maybe it's a cult leader. The cult might believe that Reid has some sort of special knowledge or power that they want to harness. They kidnap him to convert him to their beliefs or use his mind for their own strange purposes.
It could be a copycat unsub who idolizes the previous criminals the BAU has caught. He might have studied Reid's work and decided to target him to make a name for himself in the criminal world.
Another theme is Reid's own personal growth during the ordeal. He may face his fears, or learn something new about himself. For example, in some fanfictions, he discovers a new level of strength or resilience that he didn't know he had while being kidnapped.
Often, these fanfics can be a great way to expand on the relationships within the Criminal Minds universe. When Reid is kidnapped, it could bring out different sides of his relationships with his colleagues, like the deep - rooted loyalty and friendship they have for him.
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.
In some fanfictions, Reid's kidnapping could be related to his family secrets. Maybe there's someone from his past, like a long - lost relative or someone his mother knew, who abducts him to get to something valuable, either information or an object. This could lead to a lot of self - discovery for Reid as he tries to figure out the motives behind his abduction while also trying to escape.