Here's some links to my favorite hiking resources. Note, I have no sort of association with any of these websites/organizations/individuals (yay for free marketing!). These are simply the resources I saw myself utilizing time and time again when researching new trails. May they help you as much as they have helped me.
AllTrails - one of the best apps and websites out there when it comes to hiking. The app will input GoogleMaps directions to get you to the trailhead. The app also allows real time tracking of your location to determine if you are on the right trail. This is extremely useful for the many of the less-maintained hikes. While there aren't tracks for all the hikes on Hawaii, it probably covers about 95% of them (and all of the more trafficked trails).
Aloha from 808 - an awesome blog that includes a great variety of outdoor adventures. I'm a big fan of their expansive photo gallery.
Exploration Hawaii - Another great blog with some very solid hiking posts. This site is also great because it includes posts about good food spots on the island (everyone's gotta eat!).
GoHawaii - A great resource for travel to all the Hawaiian Islands. I especially like this one because it includes a lot of history about each individual island.
Hawaii Travel Guide - another awesome resource for all the Hawaiian islands. It's a good alternative to the overly touristy sites like Yelp and TripAdvisor when it comes to looking for things to do.
YouTube Channel: Hungaro Explorer - if you are a peakbagger looking to conquer some of Hawaii's best peaks, this is the YouTube channel you should check out. Nandor is on a quest to conquer and document Hawaii's 100 highest peaks. His short and simple videos give a great visual overview of what to expect.
kenjiSAITO - a really great hiking blog with a great variety of hikes. This guy is really creative in the way he connects the different ridges on Oahu and always posts about his adventures. Still active as of 2018 too!
Unreal Hawaii - pretty much the ultimate guide when it comes to hiking and other outdoor activities in Oahu. A lot of my blog is drawn on inspiration from this digital magazine.
YouTube Channel: howzitboy - a great channel with some simple videos about how to do many of the hikes on Oahu.
YouTube Channel: Not So Good Hikers - Not only do these guys have a great username, but they also put out great videos that give very good directions on how to do many of the hikes on Oahu.