Even their github https://github.com/pinterest, elixir isn't even in their top programming languages.
It could be the secret sauce language kind of deal. Or they've moved away from it.
It is a pleasure to see you outside of elixirforum.
AFAIK, Pinterest rewrote the logic of their notification system into Elixir and also used it to rebuild their rate limiter.
This is the main piece I've seen open sourced: https://github.com/pinterest/elixir-thrift