The Service Design Network has a section where you can share your own case studies. This is maybe the one specific site for service designers to post their work.

Design platforms to share your service design work

There are platforms made for visual work that work great also to present service design work like behance or dribbble

Platforms made for any types of professional

Obviously, outside of this platform, the usual players that are true for many professions are also true for service designers like Linkedin or Xing