I keep up with encryption technology and can recommend using Signal Private Messenger, the best secure messaging app that exists today. Ask your friends to use it as well.
Key features:
* The app uses your phone number as your ID. It's easy to see if a contact is using Signal too.
* Signal messages and calls are always end-to-end encrypted. No one can read your messages or see who you have been messaging with.
* Keep your chat history tidy with messages that you can set to disappear after a period of time (e.g. one week). This is great for making sure that confidential information is cleaned up.
* Send group, text, voice, video, document and picture messages.
* Make voice and video calls.
* Android, iPhone, Windows and Mac!
Install the app on your Android or iPhone device first. You can then optionally install it on a Mac or Windows PC and see your chats on PC and smartphone at the same time.