If it's on a particular fanfiction website, you could try using the search function on that site and entering the number. Maybe it's part of the title or a unique identifier there.
Finding '11577577 fanfiction' can be a bit tricky. Start by considering the most popular fanfiction platforms. If it's on a platform like Wattpad, for example, you'd want to use the search feature. You may also need to think about any related tags or keywords that might be associated with this fanfiction. If it's part of a series or has a particular author, that could also help in the search. However, without more information about what this fanfiction is related to, it's going to be a process of trial and error on different platforms.