About 5-6 years back, I searched out quite a few good fanfics of hardy boys?
1. https://m.fanfiction.net/s/3422702/1/Enemy-of-the-State
One of the best fanfics I've read, unfortunately incomplete.
2. https://m.fanfiction.net/s/1112787/1/
By the same author, again incomplete.
3. https://m.fanfiction.net/u/322808/nightwalker3
Has 2-3 amazing HB fics, but must warn, they are death fics
4. https://archiveofourown.org/users/everythingneedsrevision/pseuds/everythingneedsrevision
Another pretty decent author
I like number four, she's pretty good. I've got one going with them as ATAC (https://www.hardyboyscasefiles.com/encyclopedia.php?entry_id=1277) agents, but with Casefile (https://www.hardyboyscasefiles.com/series/casefiles.php) theme. There's been some new fic on FFN the past few days due to the HDA closing down. Check out the Hardy Boys/ Nancy Drew category again on FFN.
I will just briefly say this on fanfiction. I enjoy it in general- some of it is quite good. On the other hand, I've read some that is quite bad too. (Just speaking in general terms here- not necessarily about The Hardy Boys.) However, in the case of The Hardy Boys, there are so many official books in the series, I feel no need or desire to read fanfiction efforts. (Though I'll admit the allure of resolving loose ends does make it interesting and I feel like I may have read one years ago dealing with a return of Iola Morton [obviously set in the Casefiles universe.]) In general though, if I read fanfiction, it's usually because I'm interested to see a crossover pairing that never happened in the existing material it's based on or because I've exhausted the existing material and I'm just wanting to see more of the characters I love. (This is particularly true in the case of many of my favorite short-lived TV shows or movie series.) :) 8)
I'm very particular about the HB and ND fanfics I read, they have to be written respectfully by those who know and like the Hardy Boys and Nancy Drew characters. Sadly, not everyone does that. :( With fanfic, I like to read more stories that are like the books. I haven't found much on fanfic.net, and stopped looking there (I didn't want to sort through the garbage to find a diamond. :P) Thanks very much for the warning, goldie3. I don't like death fics and have no desire to read them. I like survival, it's exciting and inspiring. 8) There's only one place where I can recommend all of the fanfics Hardy and Drew Mysteries blog (https://hardyanddrewmysteries.wordpress.com), there are maybe about 12 on there so far, and all complete. 8) :)