From discussing potential projects to forwarding any errors in the products you’ve brought, reaching out to a specific company is a good idea.
But let’s make things a little easier by rounding it all up for you. This essentially lists (or should list) all the major companies in North America and where you can reach them, whether that’s through email or on their social media. Generally from experience, email is likely the way to go, especially if you’re in media, but sometimes reaching out on Twitter can be the best play. It doesn’t guarantee anything, but your chances are better at least.
This is broken down into three categories:
As a heads up though, this is super specific, so you’ll likely see Sol Press placed in the light novel section rather than just the manga section (so I can avoid listing things twice). But you likely know, for example, Yen Press publishes manga and LNs so just go to the manga section and grab the contact info that way.
Anime
Crunchyroll

Press requests: press@ellation.com
Billing, Store, etc: Contact page
Socials: Twitter, Facebook, Instagram
Nozomi

Press, series requests, etc: Contact page
Socials: Twitter, Facebook, Instagram
Funimation

General inquiries, subscription questions, etc: Contact page
Socials: Facebook, Twitter, Instagram
Discotek
General inquiries, interview requests, etc: Contact page
Socials: Twitter, Facebook

Sentai Filmworks

Press & News requests, screenings, etc: Contact page
Socials: Twitter, Instagram, Facebook
Media Blasters

Press and maybe other requests?: Contact page
Social: Twitter
Netflix

For most things: Contact page
For press/media things: Contact this page
Social: Twitter
Manga
VIZ Media

Donation requests, screenings, etc: Contact page
Socials: Twitter, Facebook, Instagram
Shojo Beat: Twitter, Tumblr

Media inquiries: pr@kodanshacomics.com
General questions, concerns, etc: hello@kodanshacomics.com

Editorial inquiries: yenpress@yenpress.com
Media inquiries: YenPressPublicity@yenpress.com
Socials: Twitter, Facebook, Tumblr
Denpa

Socials: Twitter
Vertical

Questions, manga requests, etc: Contact page
Socials: Twitter (LN), Twitter (Manga)
FAKKU (18+)

Any possible inquiry: contact@fakku.net
Report grammar/spelling mistake, subscription support, etc: Contact page

General or Media inquiries: info@sublimemanga.com
Site issues: support@sublimemanga.com
Seven Seas

Any questions that aren’t answered or are not portfolio pitches: Contact page
Socials: Twitter, Tumblr, Facebook
Manga.Club

Questions about their site, contact, etc: Contact page
Social: Twitter
futekiya

Socials: Twitter (DMs open), Instagram
Udon

Questions about an UDON product, etc: Contact page
Press requests: Contact this page
Dark Horse

General questions, technical questions, etc: Contact page
Socials: Twitter, Facebook, Tumblr
Light Novel

All the inquiries (sorta): info@onepeacebooks.com
Sales and distribution: scb@scbdistributors.com
Socials: Twitter, Facebook
Thanks to BP-BBP-B for the help!
Sol Press

General inquiries page: Contact page
Direct messages: general@solpress.co
Social: Twitter

Provide feedback, suggestions: contact@j-novel.club
Account questions: support@j-novel.club
Jobs in the industry: jobs@j-novel.club
Socials: Twitter, Curious Cat
BookWalker

Customer inquiries, book requests, etc: Contact page
For non-BookWalker members: support@mail.bookwalker.jp
Social: Twitter