Hermione would be extremely worried and would start researching like crazy to find out where Dumbledore has taken Harry. She would probably suspect that something is not right with Dumbledore and would try to convince Ron to help her. Ron, on the other hand, would be initially shocked but then would be ready to go on a rescue mission with Hermione.
At first, Harry would be in shock. He would be full of disbelief that Dumbledore, of all people, would do such a thing. He would struggle both physically and emotionally. Physically, he would try to break free from whatever bindings or magical restraints Dumbledore has put on him. Emotionally, he would be a mess, feeling hurt, scared, and confused. However, depending on how the story unfolds, he could gradually come to terms with the situation if Dumbledore manages to convince him that it's all for a greater good.
The Ministry of Magic would probably be in an uproar. They might see Dumbledore's actions as a blatant abuse of power. They would send out Aurors to search for Harry and arrest Dumbledore. After all, Dumbledore is one of the most powerful wizards, and his actions would be seen as a threat to the stability of the wizarding world.
Percy would be really angry. He's used to being in control of his own situation, and being kidnapped is not something he would take lightly. He'd probably try to fight back right away, using his demigod powers like his sword fighting skills and his ability to control water.
At first, Harry may be in shock. He's been taken by someone he respects and looks up to. As he comes to terms with his situation, he might try to reason with Dumbledore. If that doesn't work, he could start to plan an escape, using his wits and the magic he knows. He might also feel angry that Dumbledore is treating him this way when he's always been on Harry's side, or at least that's what Harry thought.
Hermione would be horrified. She would immediately start trying to figure out a way to rescue Harry. She might start researching in the library for some ancient spells or forgotten magic that could help. Ron would be angry at Dumbledore and would probably want to rush off to save Harry without much of a plan at first.
Well, Dumbledore might be more understanding. He knows Snape has his own motives and might suspect that there's more to the kidnapping than meets the eye. He would try to talk to Snape first. The other teachers would be divided. Some would side with Harry and think Snape has gone too far, while others might wait for more information. The students would be in an uproar, especially those who are friends with the kidnapped person. They'd form groups to try and find out what happened and rescue their friend.
At the beginning, Harry would be frightened. He's in an unknown place with Loki, who is known for his trickery. But Harry is no pushover. He would quickly gather his courage. He would remember all the times he's faced danger at Hogwarts. He might try to communicate with Loki to understand his motives. If Loki reveals that he wants to use Harry's magic for something, Harry would try to find a way to outsmart Loki. He could pretend to cooperate while actually looking for a weakness in Loki's plan. Harry would also be thinking about his friends at Hogwarts and how he needs to get back to them, which would give him extra motivation to fight back against Loki.
Max would likely be initially shocked but then quickly start looking for ways to outwit his captors. He'd be making mental notes of everything in the room, like the layout, any possible exits, and what the kidnappers look like.
Hiro would be determined to save the kidnapped member. He'd immediately start analyzing the situation, using his intelligence to figure out where they might be held. Baymax would be concerned for the safety of the kidnapped character and would follow Hiro's lead. GoGo would be angry and ready to take action, using her speed to quickly track down any leads. Wasabi would be a bit more cautious but still committed to the rescue. Fred would probably be coming up with wild but potentially useful ideas on how to save their friend.
Harry might initially be confused. He has always looked up to Dumbledore, so when he realizes Dumbledore is trying to control him, he could start to question everything he thought he knew about their relationship. He may become more rebellious as a result, trying to break free from Dumbledore's influence and make his own decisions.