The other students at Hogwarts would be in an uproar. Harry is a hero to most of them, so the idea of him kidnapping Ginny would be hard to believe. Some would be in denial, while others would form groups to search for Ginny. The Gryffindor students especially would feel a sense of responsibility to rescue one of their own.
Ron would be furious. He would immediately start looking for Ginny and would probably want to confront Harry without thinking. Hermione, on the other hand, would be more rational. She would try to figure out why Harry would do such a thing and look for clues. The Weasley parents would be extremely worried and would likely reach out to all their contacts in the wizarding world for help.
The wizarding community at large would be divided. Those who have always been skeptical of Harry, like some of the pure - blood supremacists, would use this as an excuse to smear his name further. However, Harry's true friends would be desperate to prove his innocence or, if he is actually guilty, to help him come to his senses. Ginny's friends, like Luna, would be worried sick and would do whatever they could to get her back safely.
Naruko herself would probably be shocked at first, but then she would start trying to reason with Sasuke. She would ask him why he's doing this and try to make him see that whatever he's thinking is wrong. She's a strong - willed character and wouldn't just sit there passively.
Ginny often reacts with defiance. She's a strong - willed character. So, she might fight back against Dark Harry, both physically and verbally. She could try to escape at every opportunity, using her knowledge of magic to her advantage.
At the start, Ginny would be shocked and terrified when Tom Riddle kidnaps her. However, as time passes, her Gryffindor courage would kick in. She would start to analyze Tom Riddle's motives and actions. She might pretend to be more vulnerable than she actually is to lower his guard. Ginny could also try to communicate with any magical creatures or objects in her vicinity for help. And she would be mentally preparing herself for a fight or escape, using every bit of her magical training and her wits to outsmart Tom Riddle.
Stefan would be extremely worried and angry. As Elena's other love interest, he has a deep connection with her. He would immediately start looking for her, using all his vampire skills and resources. He would probably suspect Damon right away, given their history of rivalry over Elena.
Ginny would likely be heartbroken. She's a strong character but she loves Harry deeply. She might start to question herself and what she did wrong. Cho, on the other hand, would be surprised but also happy. She may have still had feelings for Harry all along. Harry himself would be conflicted at first, feeling guilty for leaving Ginny but also excited about the possibility with Cho.
Naruto would be extremely enraged. He would vow to rescue Sakura no matter what. He would immediately start gathering his friends and form a rescue team. Sasuke, on the other hand, might initially seem more reserved but would also be determined to get Sakura back. He would use his Sharingan skills to track Madara.
Their friends would be in shock. Ron, being Harry's best friend and Ginny's brother, would be torn between loyalty to both. Hermione would probably be disappointed in Ginny and very supportive of Harry. The Weasley family as a whole would be divided. Mrs. Weasley, who loves Harry like a son, would be heartbroken and angry at Ginny. Their other friends at Hogwarts or in the Order of the Phoenix would likely gossip and have mixed feelings. Some might pity Ginny for the difficult situation she got herself into, but also condemn her for cheating on Harry.
The other Hogwarts students would have a wide range of reactions. Some might be shocked and gossip about it. Neville, for example, might be sympathetic towards Harry. Draco Malfoy could use it as an opportunity to taunt Harry, but at the same time be a bit envious of the attention this situation brings. The teachers would also have different responses. McGonagall might be worried about the impact on Harry's education and future.
Harry would likely be determined to stop it. He has faced many dangerous situations before, and this would be just another one for him to overcome. He might be a bit scared at first, but his sense of responsibility would kick in. Hermione would immediately start researching, trying to find any information about how to deal with such a strange combination of magic and a weapon like a nuke. Ron would be ready to support his friends, perhaps with some humor to lighten the mood in such a tense situation.