For better user experience, Hidden Chat has been upgraded to Invisible Friends.
To turn on/off Invisible Friends,
you could enter[Me] page -[Privacy & Security]- modify [Invisible Friends].
To find out your invisible friends,
you could tap the search icon in imo homepage
-Enter""#"" and your password.
Note:
This feature is still under test and will gradually open to more users.
If you still can't find it on the latest version,
please expect it later.