His friends could use their various quirks to track him. For example, if there are characters with enhanced sense of smell or the ability to detect energy, they could start the search. Then, they would plan a strategic attack on the kidnappers' hideout.
First, the heroes would gather intelligence about the kidnappers. They might look for any clues left at the scene of the kidnapping. Once they have an idea of who took Deku and where they might be, they would form a team. This team would consist of heroes with different skills. Some would be good at combat, while others might be better at stealth or negotiation. They would then execute a well - planned rescue operation.
In fanfiction, if Deku gets kidnapped, his friends from U.A. High would likely launch a rescue mission. Bakugo might be especially determined, as much as he tries to hide his concern. They would use their quirks in creative ways to track Deku down.
His friends could come to the rescue. Bakugo, for instance, might use his explosive power to break into Toga's hideout. He's always been competitive with Deku, but he also cares about him deeply.
Dean and Cas could use their combined skills. Dean's hunting expertise and Cas's angelic powers would be a great asset. They might track down the kidnappers through some supernatural means like following a magical trail or using Cas's ability to sense Sam's location.
The Wild Kratts team could use their animal powers to rescue Martin. For instance, if they had the power of eagles, they could fly over the area where he might be held and look for any signs of him.
He might cry a lot. Deku is very emotional, and being cheated on would be a very painful experience for him. He could also get angry, which is rare for him, but this situation would be so unjust that he might not be able to hold it in. He'd probably start to question his self - worth too, thinking that there was something wrong with him that made his partner cheat.
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.
Nico could initially be shocked and scared. But as he regains his composure, he would likely start to analyze the situation. He might try to communicate with the Avengers, especially if he realizes they are not pure villains. He would use his wits to find a way out of the situation while also trying to understand their motives for kidnapping him.
He could use his Rasengan. If he manages to gather enough chakra secretly, he can surprise his captors with a powerful Rasengan and break free.
The other Teen Titans could also play a big role in the rescue. Starfire could use her powers to fly in and distract Slade while Cyborg and Beast Boy create a diversion. Raven could use her magic to break any spells or traps that Slade has set for Robin. They would all work together as a team to get Robin back safely.
The police need to be involved. They should start an immediate investigation, following any leads like eyewitness accounts or ransom demands.