Facebook, WhatsApp and Instagram were all investigated by the Data Protection Commission last year.
They were among 15 tech companies looked into by the watchdog over their compliance with GDPR.
The Data Protection Commission's annual report shows just over 4,700 valid breaches were reported to it between May and December 2018.
That's a 70% rise in the number of data breaches in Ireland since new GDPR laws were brought in.
More than 2,800 complaints were made to the office - a 56 % increase on the year before.
Graham Doyle, from the Data Protection Commission, said all of those investigations are ongoing.
"There into six different companies," he said.
"There are nine of those inquiries that were opened that are complaint based inquiries, and then we had another six inquiries that we opened of our own volition.
"Some of them are a results of individual breach notifications."