In this type of fanfiction, it's possible that a new character could be introduced as the rescuer. Maybe a powerful witch who has been watching Stiles from afar and decides to intervene. Or an old acquaintance of Gerard's who has a change of heart and helps Stiles escape. However, the core group of Stiles' friends and family still remain the most likely candidates. They know him best and have the most motivation to get him back safely. For example, Scott's loyalty to Stiles is unwavering, and he would go to great lengths to save him, using his werewolf abilities and his knowledge of Gerard's past actions.
His friends, of course. Scott would be one of the most likely rescuers. As Stiles' best friend and a werewolf, he has the strength and loyalty to track Stiles down. Lydia might also be involved. With her banshee powers, she could sense Stiles' distress and lead the others to him. Another possible rescuer could be Derek. He has a lot of experience dealing with dangerous situations and might feel a sense of obligation to save Stiles, especially if he realizes Gerard is involved.
Stiles' father could be a potential rescuer. He's a cop and would be determined to find his son. He might use his police resources and connections to track down any leads on Gerard and Stiles. Also, the pack that Scott is a part of would all be likely to help. They see Stiles as part of their group, and they wouldn't let one of their own be in Gerard's clutches for long. Even some of the more minor characters in the show who have a connection to Stiles might step up, like the Sheriff's deputies who could unknowingly stumble upon a clue that leads to Stiles' rescue.
Chapter 348, "Schemes and Counter-Schemes, the Five of East Ridge, Zhu Yang's Threat, The Dust Settles (Part 4)", is the clearest early answer because it turns Luo Cheng's situation into a concrete plot event. The setup is Upon hearing that Yanggu had sent someone first, Lu Yang raised his..., but the pressure keeps building through Just said to cooperate with us, East Ridge, and now he's betraying....
Chapter 338, "Rapid Progress, Martial Arts Skills, Dual Eastern Advances, Dormant Phase 6", is the clearest early answer because Xia Chuan finally turns buildup into a real advancement. Early on, At that time, we only need to keep the secret of the hidden passage,.... By the end, This Cold Wing Sword was crafted by Mu Dong last month..
Chapter 394, "I'll Invest One Billion in Your Movie", is the clearest early answer because it turns Wilderness Survival's situation into a concrete plot event.
Chapter 79, "Finally, I'm not the last one anymore!", is the clearest early answer because it turns Commodity Trading Law's situation into a concrete plot event. Early on, Jiang Li leisurely said, "I bought this weeding machine, and....
Chapter 28, "Beaten Up Again", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. Early on, The next evening, Jiang Yan drove home seething with rage.. By the end, Lili then kicked his knee hard..
Chapter 37, "Those in the know anticipate the transformation, while the oblivious think it's a fashion show.", is the clearest early answer because it turns Director Sun's situation into a concrete plot event.
Chapter 73, "Does Someone Like Jiang Li Deserve to Have a Fan Club?", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event.
Chapter 133, "Teacher Du, Please Reconsider the Termination of the Contract", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. It opens with Watching Jiang Li and the others finish their meal and tidy up the...
Chapter 287, "Saved", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, For five consecutive days, the search and rescue team had not.... By the end, Failing to obtain any news after numerous attempts, Lu Xingchao had....
Chapter 37, "Those in the know anticipate the transformation, while the oblivious think it's a fashion show.", is the clearest early answer because it turns Flash Change's situation into a concrete plot event.