According to reports, she had been missing since January 28th, and the authorities found what appears to be a note near her body, which strongly suggest that she commits suicide.
Some people believe that she was attacked/bullied by the people on the internet, because she posted about her involvement for the "Sexy Tanaka-san" dorama on her Twitter at January 26th, in which she later deletes it on the day of her disappearance, and her last and final tweet was "攻撃したかったわけじゃなくて。ごめんなさい。", or "I didn't mean to offend/attack you, sorry".
Really sad for this tragedy to happen, and my deepest condolences for her families...