Maybe it's a group of supervillains who have joined forces. They realize that Tony and Peter together are a big threat to their plans. So they kidnap them to try and keep them out of the way. This group could include the likes of Vulture, who has a personal vendetta against Tony, and some other villains who are just after power and see Tony and Peter as obstacles.
The Mandarin could be a likely kidnapper. In the Iron Man universe, he's a powerful and devious enemy. He might see value in capturing both Tony and Peter. He could use Peter to manipulate Tony into doing something for him, like building a new weapon or giving up some valuable technology secrets.
It could be some disgruntled former employees of Stark Industries. They might feel that they were wronged by Tony in some way, like being fired or not getting the credit they deserved for their work. And they see kidnapping him as a way to get revenge. Peter might just be collateral damage since he is associated with Tony.
One group that could be the kidnappers are AIM (Advanced Idea Mechanics). They're always interested in getting their hands on advanced technology, and Stark has plenty of that. The Ten Rings terrorist organization is also a possibility. They've targeted Stark before and kidnapping him again would be a way to make a big statement. And let's not forget some rogue elements within S.H.I.E.L.D. who might think that Stark is a threat and kidnap him to keep him in check.
The Green Goblin is a likely kidnapper. He's always had a vendetta against Spider - Man. Also, Doctor Octopus could be a candidate. His mechanical arms and his intelligence make him a formidable foe who might kidnap Peter for his own devious experiments. Another one could be the Vulture, who might see Peter as a valuable asset to sell to the highest bidder in the criminal underworld.
Another possibility is some disgruntled former employees. Maybe they feel they were wronged by Stark and want to get revenge. They know his routines and weaknesses well enough to plan a successful kidnapping.
Well, they could be kidnapped by a mad scientist. The scientist might be interested in Peter's spider - DNA and Tony's Iron Man suit technology. Once kidnapped, they would first try to assess their situation. Tony would probably look for any weak points in the confinement area, while Peter might use his spider - sense to detect any incoming danger or opportunity for escape.
A fanfiction might involve Peter Parker and Tony Stark being kidnapped during a mission. They are held in a high - security facility. While kidnapped, Tony uses his wits to analyze the security system, and Peter uses his enhanced senses to gather information about their captors. Eventually, they manage to outsmart their captors and escape.
It could be a vengeful god or goddess. Maybe one who has a grudge against the demigods in general and sees Annabeth as an easy target to send a message. For example, a minor god who feels overlooked and wants to prove their power by kidnapping such a well - known demigod.
One possible motive could be money. The Stark family is wealthy, so the kidnappers might be after a large ransom. They could think that by holding Peter captive, they can force Tony Stark to pay up a huge sum.
The Joker is a likely kidnapper. He has a history of causing chaos and targeting the Bat - family. He might see kidnapping Batgirl as a way to get back at Batman or just for his own twisted amusement.
It could be a group of rogue ninjas. They might see Shikamaru as a valuable asset due to his intelligence and strategic skills. They could plan to sell him to the highest bidder or use him to carry out their own devious schemes.
It could be a rival athlete who is jealous of Serena's success. They might think that by kidnapping her, they can eliminate the competition. Another possibility is a deranged fan who has an unhealthy obsession with Serena and wants to keep her all to themselves.