This was suggested in another thread recently that I browsed on Reddit https://www.reddit.com/r/HungryArtists/
You should also advertise on your social media networks just in case. Using hashtags may help people find your posts as well
Example (Twitter): Hello, I am a writer and artist looking to #hire a #comic #artist for a grim story idea. I'm looking for someone who can do black and white #manga style, like this: LINK. DM me for further details if you're interested!
Example (Tumblr): Hello, I am a writer and artist looking to hire a comic artist for a grim story idea. I'm looking for someone who can do black and white manga style, like this: LINK. Reblog/Message me for further details if you're interested!
Tags (top 5): artists on Tumblr, comic, comic artist, hiring, freelance (then any keyword you add to your post can be searched for automatically, so I'd also add these tags at the bottom of your post in case people search by keyword and not tags)
I don't know how Facebook posts are found, but use their hashtag/search system
Anyway, good luck finding someone! I went ahead and linked to this thread on my Twitter for you too (: