I don't know about JE stars having blogs, but I do know that many of them write jwebs that fans subscribe to through their mobile phone. The service is only available to Japanese fans but there are people who translate and upload them onto the internet for us poor overseas fans.
For folks like Arashi, NEWS, Kanjani8 and KAT-TUN, their jwebs are tranlsation over at
Binan no Nikki (which basically means Pretty Boy's diary). The translation can be quite irregular for some members, but folks like Massu, Tegoshi and Nino's jwebs are updated pretty regularly.
Over at
Umi no Namida, Yamapi's jwebs and monthly article gets translated regularly alongside with blog entries of the author who's a major fan of Yamapi and Ikuta Toma. She said pretty insightful things sometimes, and can be pretty hilarious as well. However, she locked her blog recently as some folks had been flaming her as she made some comments about not liking KAT-TUN. You can get the password to her blog by emailing her.
Binan no Nikki
Umi no Namida