You can start with Weibo. You can get a Weibo account with a phone number or email address. Many famous US brands or celebrities have a Weibo account nowadays. Some of them have more followers on Weibo than on Twitter :)

Some may argue that Wechat's official account is better than Weibo in terms of reaching users & engagement, as every Chinese internet user is on Wechat now. But it's tedious to get an Wechat official account: https://admin.wechat.com/

Old school email newsletter may work for reaching well-educated Chinese internet users. However, Chinese people don't use email much. Again, everyone's on Wechat.