Can junior high school students use WeChat to ask for leave from their teachers?

Yes, it depends on your class teacher.

A normal vacation is fine. Just send your actual reason for leave to the teacher on WeChat. Teachers are generally allowed to ask for leave. When sending WeChat, the text content should be clear and organized, and there should be respect for the teacher. Ask for leave and be realistic, that's all. There is no need to hide or change some reasons that you don't have. Just seek truth from facts and be sincere. If you ask the teacher for leave, you should explain the reason, then why and when to go back to school, then ask your parents to send a text message to the teacher, and then you will be fine.