Is this a breach of privacy?

[Oh_hunnihunni]

No. The clue is in the word social - the relationship is an open, public, social one, with no justifiable expectation of privacy.

Under Principle 11, an agent must restrict their use of personal data to the business that data has been supplied for. So, the harvesting of data from social media is part of that business, just as the people posting and hosting expect it to be. Posters want to be heard. They are being heard. And responded to.

It isn't a private transaction.