Neville is also quite popular. His growth from a somewhat clumsy and timid student to a brave and confident member of Dumbledore's Army is a great source of inspiration. In fanfics, he might be given even more heroic moments, like leading the group in a crucial battle or discovery.
In some fanfics, Dumbledore's Army could be involved in secret missions outside of Hogwarts. For example, they might go on a quest to find a hidden magical artifact that could help in the fight against Voldemort. This would add an element of adventure and mystery to the story.
There's also a chance that Dumbledore gets caught by a group of rogue magical creatures. For instance, if he was exploring an area that was supposed to be off - limits to wizards and the creatures there saw him as an intruder. They might not be as rational as wizards and could hold him captive without really understanding who he is.
Well, it could be that Dumbledore has some sort of hidden device or spell that he activates when kidnapped. For example, he could have a charmed object that sends a signal to his allies, like the Order of the Phoenix. His allies then come to his rescue and he manages to escape during the chaos. Also, Dumbledore is extremely intelligent. He might outwit Grindelwald by engaging him in a complex conversation full of riddles and misdirections, which gives him an opportunity to break free.
The Journey to the Army was a group of poems by the Tang Dynasty poet Wang Changling, with a total of seven poems. This set of poems depicted the homesickness of the border guards and their ambition to protect their homes and defend their country, showing the combat effectiveness of the Tang army and the atmosphere of the prosperous Tang Dynasty. The poem described a soldier sitting alone on the tower, feeling the autumn wind blowing from the lake at dusk. It also depicted the scenes of Qinghai's Changyun Dark Snow Mountain and the isolated city looking at the Jade Gate Pass, as well as the war scenes of the desert and the red flag rolling out of the Yuan Gate. This set of poems, with its tragic style and touching emotions, moved people and made them feel the loyalty and sacrifice of the soldiers guarding the border.
The main character was a modern doctor. After transmigrating, she became the useless eldest daughter of the General's Estate. Because she was killed by someone, the people wanted to kill her.
It could be Severus Snape. He has a complex relationship with Dumbledore. Maybe Snape discovers some of Dumbledore's plans that he doesn't agree with regarding Harry Potter. He then sends a Howler in a fit of anger to express his disapproval.
In a fanfiction, Dumbledore might steal out of desperation. Suppose there was a situation where a curse was about to be unleashed on Hogwarts, and the only way to stop it was by stealing a particular ingredient for an antidote from a place where it was not supposed to be taken. Dumbledore, seeing no other option, decides to steal it. His motive here is to save the school and its students, even if it means breaking the rules.
Fred and George Weasley are very likely candidates. They are known for their love of pranks and their mischievous nature. They might see pranking Dumbledore as the ultimate challenge.
Dumbledore, as Harry's guardian in the fanfiction, would probably use his influence in the wizarding world. He could make sure that Harry is taught by the best teachers at Hogwarts. He'd also be there to offer advice and guidance, especially when Harry faces challenges like dealing with Voldemort or other dark forces. For example, he might teach Harry some advanced defensive magic privately to better protect himself.