At least 21 people were detained as part of an investigation into the Gülen movement in Zonguldak, on Friday.
Among the detainees are university students, shopkeepers and former public servants. Detainees are accused of using ByLock.
Turkish authorities believe using ByLock is a sign of being a Gülen follower as they see the mobile phone application as the top communication tool among the group.
Meanwhile, 18 people including imams, teachers, engineers and bankers were detained as part of a separate, Ordu-based investigation over similar charges the same day.
Tens of thousands of civil servants, police officers and businessmen have either been dismissed or arrested for using ByLock since the failed coup attempt.
The military coup attempt on July 15 killed 249 people and wounded more than a thousand others. Immediately after the putsch, the Justice and Development Party (AKP) government along with President Recep Tayyip Erdoğan pinned the blame on the Gülen movement and initiated a widespread purge aimed at cleansing sympathizers of the movement from within state institutions, dehumanizing its popular figures and putting them in custody.
Turkey’s Justice Ministry announced on July 13 that 50,510 people have been arrested and 169,013 have been the subject of legal proceedings on coup charges since the failed coup.