When to use?
Sending messages through Signal is pretty safe. There is also the possibility to erase messages on the sender and receiver's devices after some time. If you want to be more sure you can also buy a new SIM card that can be used on the Signal app.
If you are sure that your phone is safe and you want to share information about suspicious events concerning minor migrants, you can send a Signal message to Lost in Europe at this number: +31 622263260
Signal is an open-source app to send encrypted messages via mobile. You can download the app here.