UI Faces aggregates various free avatar placeholder sources that you can use in your design
mockups by copy—paste, API, plugins for Sketch, Adobe XD and Figma.
EDIT : site is up again and works well. It's a one trick poney but well done. I love the abstract faces a lot. I hope it will be updated soon to include more faces.
Product Hunt had a wrong link on the listing. It's fixed now, the link to the website is https://uifaces.co
EDIT: Thank you very much for the updated review 🙇♂️
Design Buddy