However, police later said that a "fake account" was used by unidentified person or persons in the teenager's name.
"We have received a complaint against a person that he posted some objectionable comments against Raj Thackeray on Facebook. We are questioning him as we do not want to repeat the same mistakes committed a few days ago," an officer at Palghar police station told PTI, speaking on condition of anonymity.
The boy has not been charged and police have sought legal opinion, he said.
Kundan Sankhe, president of Thane rural unit of the MNS, has claimed the boy had made "vulgar" comments about Raj Thackeray, and the people of Maharashtra, including women.
Late in the night, Additional Superintendent of Police, Thane, S Nishandar told PTI that as per the probe, some unidentified person created a fake account in the name of Sunil Vishwakarma, and posted objectionable comment about Thackeray and Maharashtrians in his name.
Vishwakarma (19) had accessed his own Facebook account last on Monday, while the comment on fake account was posted the next day.
"Vishwakarma is helping us. We have registered a case against unidentified person," Nishandar added.
The incident came close on the heels of the arrest of two girls at Palghar over a Facebook comment by one of them on the shut-down of the city following Shiv Sena chief Bal hackeray's funeral.