Supervisor published my thesis figures without including me as an author
is this academic misconduct?


That depends. Your thesis is published, just not in a journal. It’s published as part of your alma mater’s repository and anyone can access it, your advisor in particular. Regarding the figures: it really depends on how they did it. If they copied them without citing your thesis that’s pretty clear cut plagiarism which is wrong under any standard of academic publishing. If they cite you (saying something like figure taken from X), that should probably be okay. This is especially true if your advisor helped design and generate these figures (they’d be a coauthor of sorts). Again, you should be credited regardless, and if a citation is missing it should be noted. I’d be extremely surprised if your advisor wouldn’t be willing to cite you, my guess is that the student who wrote the paper forgot to (remember hanlon’s razor!).


  what is the appropriate avenue to correct this?


You could first try and reach out to your former advisor. Ask them. Maybe there’s a simple misunderstanding here. If there’s a dispute the most direct course of action is reaching out to the department head, or vice dean of research and inform them. If you have contacts on the department (a trusted professor who’s sufficiently senior), might be good to hear their opinion on the matter. 

Contacting the journal or anyone external should be a last resort I think. But if you feel like you’ve exhausted your options with the department and nobody’s listening, it may not be a bad idea. Again, expect a laconic response: some journal editor will be extremely hesitant in dealing with such cases, especially since the paper is out.

Good luck!

EDIT: I missed this part


  the other student has replicated one of the chapters of my PhD thesis


That is unacceptable plagiarism even with citation. Lifting entire chapters (even paragraphs) is never okay. The figures are a much more minor issue. Start with that!