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.
In this kind of fanfiction scenario, Dean and Cas's relationship could be the key to rescuing Sam. Their growing bond might give them an extra boost of power or determination. They could communicate on a deeper level and figure out where Sam is being held. Once they find the location, they would have to fight their way through whatever guards or traps the kidnappers have set up. It could be a long and arduous process, but their love for Sam and for each other would drive them to succeed.
In a Destiel - centered fanfiction where Sam is kidnapped, perhaps it's all part of some grand scheme to make Dean realize his true feelings for Cas. The kidnappers might be some over - zealous fans within the story who think that by causing chaos, they can bring about the Destiel endgame. They could hold Sam in some strange, other - dimensional location and send Dean and Cas on a quest to find him.
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.
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.
One way could be a stealth mission. Shikamaru, with his high intelligence, could plan a strategy to infiltrate Kumo's hideout undetected. He could gather a small team of skilled ninja like Neji (if he were still alive in the fanfiction), Rock Lee, and Ino for mind - reading and communication. Then they could free Naruto and Hinata and escape before Kumo realizes what's happening.
Joel could use his combat skills and stealth to infiltrate the place where Tess is being held. He'd probably take out the guards one by one and then free Tess.
The Sailor Guardians could start by using their powers together. Sailor Moon could use her Moon Healing Escalation to try and sense any dark energy around where Michiru was last seen. They could also split up and search different areas. Maybe Neptune's own powers could be used in some way to call out to her or track her down. Once they find the location, they would fight off the kidnappers using their combined attacks.
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.
In fanfiction, if Sam was kidnapped, it could lead to a very intense story. Dean would surely go on a rampage to find him. Maybe Sam was kidnapped by a powerful demon who wants to use him for some dark ritual. It could also be a new, unknown enemy who has a vendetta against the Winchesters.
Yusuke could use his spirit detective skills to track down Keiko. He might fight his way through Sakyo and Toguro's minions to reach her.
Naruto could try to befriend some of the Kumo ninjas who might not be in favor of the kidnapping. By winning them over, they could help him escape. Also, he could use his knowledge of ninja techniques and his quick thinking. For example, he could use substitution jutsu to switch places with an object when the guards are not looking and then make a run for it.