How to get in contact with a manga author?

[lisa]

I want to write a letter to a manga author I like very much, but how do I do it?

I would like to get in contact with these authors:
Kumagai Kyoko
Tachibana Higuchi

[Edward]

the fastest way to get in touch with those authors is through social networking sites like facebook, twitter and instagram, but i doubt they have instagram.
i'm sure they have facebook and twitter for the purpose of interacting with fans and also for the fans to be updated for their recent release and recent works.
writing a letter, as in paper letter is quite hard ( but not impossible), because we want also to respect their privacy.