do go on please continue (if they have been interrupted) You were saying? or What were you going to say? Inviting someone to speak, Do you have anything (else) to add?

-If you want a person to express the opinion. You could say, "would you like to share?", - inviting a person for a discussion: "(would you) care to join (us)?" -or you want a person to continue the idea: "could you expand on that? ", "do go on", "go ahead".

I guess something like "Please keep going" or "Please continue" works as well