Here's what you do.
You go to your JAV source site of choice, usually they have the actress' name written in Kanji and if all else fails you just go straight to DMM.
You then copy & paste that name into Google and there you have it, her social media accounts should be among the first links.
If not, you visit ja.wikipedia.org and search for the name there. Usually their Wikipedia Entry will have all the necessary links. In some cases you can even find the new accounts of retired actresses. This is how I found Ayu Sakurai's post-AV account for example.
https://twitter.com/yoshimi_mio