how can I get the Messenger id from a user by using Facebook API?

i have a question

Is it possible to get user id from Facebook groups or pages using the API for connect to the messenger id?

I am creating an app for my thesis project and I need to do the next things:

1. select some posts and analyze them using my algorithm – I have this posts in my app
2. I would like to send directly to the MESSENGER OF THAT PERSON (who wrote the post)

For example.
1º Hello, I am selling a flat
2º click the button: open a chat with that person in Messenger.

I wanted to take the email but it’s not possible.

Thanks in advance,
Armando