In fanfiction, if Naruto gets kidnapped by Akatsuki, he might be used as a bargaining chip. The Akatsuki could try to exchange him for something valuable like the Nine - Tailed Fox's chakra. Or they might try to extract the Nine - Tails from him forcefully. Naruto would surely put up a fight though, using his Rasengan and other jutsu.
In fanfiction, Naruto has a lot of ways to escape from Akatsuki if kidnapped. He could wait for an opportunity when the Akatsuki members are preoccupied with their internal disputes. Since he has a strong bond with his friends in Konoha, they might be on their way to rescue him. Naruto could also use his unique Uzumaki bloodline abilities, like his strong life force, to endure any torture or imprisonment until he finds a way to get out. He might even discover some secrets about the Akatsuki during his captivity that could be used to his advantage.
If Sakura gets kidnapped by the Akatsuki in fanfiction, Sasuke could also get involved. Since he has his own history with the Akatsuki, he might use his knowledge to track them down. Also, Sakura herself could be trying to find a way to escape from within. She's a strong kunoichi, after all. She might be gathering information about the Akatsuki's plans while being held captive.
Naruto could use his shadow clones to create a diversion. He might make a bunch of clones and have them attack the Akatsuki members in different directions while he tries to find a way out. For example, he could use the chaos to search for a hidden passage or a weak spot in their hideout.
Naruto would definitely fight back. Despite being kidnapped, she has a strong will and a lot of chakra. She would use her Shadow Clone Jutsu to create distractions and try to break free from her captors. And she would also be yelling at them, trying to get them to see the error of their ways.
One possibility is that the Akatsuki members might try to extract information from her. Since Naruto has a lot of knowledge about the Hidden Leaf Village. Maybe they want to know about the Nine - Tails inside her. However, Naruto is very stubborn, so she would likely resist their interrogation attempts.
It could be Orochimaru. He has always been interested in Naruto's power and potential. He might kidnap Naruto to try and extract the Nine - Tails' chakra or study his unique Uzumaki bloodline further. Another possibility is a group of rogue ninjas who want to sell Naruto to the highest bidder, thinking his value as a Jinchuriki would make them rich.
Well, in most cases, his friends would likely try to rescue him. Sasuke might put aside his differences for a while and join forces with Sakura and the others. They'd probably start by gathering information about the council's motives and the location where Naruto is being held.
Naruto would be angry. He's not the type to just accept being kidnapped. He'd immediately start looking for ways to escape. He might try to use his ninja skills to break free from whatever restraints Orochimaru has put on him.
Maybe the Akatsuki members who kidnapped Naruto start to have second thoughts. Some of them might realize that Naruto is not just a tool for their goals. They could begin to see his value as a person and his potential to bring peace in a different way. This could lead to internal conflicts within the Akatsuki group.