A good way to link with Wechat groups is to seek out those related to your interests. Last year, for example, I asked if there were any cycling groups in Kunming. I made the request on GoKunming, and I received a few PMs that allowed me to link to three Wechats.
Some groups may be reluctant to respond to an open 'add me to any group' type message. In part because once a group gets over a certain size there are legal limitations (and responsibilities) that apply to Wechat groups.
These groups are often very specific, e.g. parents group, kinder-garden, teachers group, teacher recruitment, etc.
I also find that every time I have put my Wechat ID into a post, I have received commercial traffic. The GoKunming forum is a good starting place for questions, and they filter out the SPAM for you.