It could be Draco Malfoy. He's always been a bit of a troublemaker when it comes to Harry. Maybe he used a spell to knock the glasses off Harry's face during a confrontation in the hallway.
His friends, Hermione and Ron, would surely help. Hermione with her intelligence and Ron with his loyalty.
Maybe while he's feeling for his glasses, he stumbles upon a hidden object or a clue. This could be related to a mystery he's currently involved in within the fanfiction world. It could be a key to unlocking a secret chamber or a message from an unknown sender.
He could try to trick the Snatchers into giving them back. Maybe he pretends to be more injured or incapacitated than he really is, and when they come close to check on him, he quickly grabs his glasses back.
If the Snatchers made Harry lose his glasses, it would be a big change. Harry has always been the one with the glasses, the boy who lived. Without them, he would be in a state of confusion and disorientation. His reactions to the Snatchers would be different. He might be more panicked and less able to strategize. And his friends would have to take on more of a protective role. Also, it could lead to some interesting interactions with magical creatures or objects that could help him regain his vision or at least function better without his glasses.
In this fanfiction, his glasses could have a disorder where they constantly fog up, no matter the temperature or humidity. It would be really annoying for Harry. He might be in the middle of a battle with Death Eaters or trying to solve a mystery in Hogwarts, and he has to keep wiping his glasses to see clearly.
One popular 'Harry feeling for glasses' fanfiction might be 'The Lost Spectacles'. In this story, Harry loses his glasses in the Forbidden Forest and his frantic search leads to some unexpected magical encounters. It has a great blend of adventure and the charm of Harry's clumsy yet endearing search for his glasses.
Perhaps it's an old enemy from Harry's past, like Draco Malfoy who has turned to the dark side completely. He blames Harry for all his misfortunes and decides to cage him without his glasses as a form of cruel punishment.
Obviously, Harry Potter himself would be at the center of it. His friends Ron and Hermione would likely be involved too. They might be trying to protect Harry or stop him from getting into more trouble. Also, Draco Malfoy could be involved. He might take advantage of Harry's lack of glasses and start a fight, thinking he can easily defeat Harry when he's not seeing clearly.
It could symbolize his vulnerability. Without his glasses, Harry can't see clearly, which makes him more defenseless in this chained - up situation.
There's 'Harry's Glasses: A Comedy of Errors'. Here, Harry's search for his glasses is made even more difficult by his friends' well - intentioned but ultimately bumbling attempts to help him. The author uses a lot of witty dialogue and slapstick - like situations to create a really humorous take on the simple act of Harry looking for his glasses.