I thought there was already a thread like this one. Also, it's mostly twitter and Instagram rather than blogs and Facebook nowadays. Some even have YouTube accounts.
^I know some of them deleted their social media accounts, open new ones, or clean their history after retiring or when they got hit by a scandal like drugs.
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
My jav link is javlibrary.com and r18.com
There is no japan version, only english language.
Uh, you can totally switch to japanese on Javlibrary.com. In the upper right.
And then there's DMM.
http://www.dmm.co.jp/digital/videoa/-/actress/recommend/
If they want to redirect you to R18, switch the language to japanese. The physical media section is region locked, but you can freely browse and buy from their digital section.