Nabeel Masih was arrested for liking an "inappropriate" photograph on Facebook. He is accused of blasphemy charges for clicking the like button under an image of the Kaaba in Mecca, one of the holiest sites in Islam.
A Muslim alerted officers to the post saying he found it insulting to his religion, police said.
The teenager has been held in custody ahead of a trial. If found guilty he could face the death penalty.
Aneeqa Maria Anthony, head of the legal team representing the boy, said she was told by a lawyer for the Muslim to "watch herself and stay away".
A group of people attending a court hearing also threatened Masih's family.
During the hearing Amin Muzammal Chaudhry, a lawyer for the Muslim, said: "This man has blasphemed against Islam.
"You should know that Pakistan is an Islamic state. We are all Muslims. These are Muslim courts, so you should not defend such a criminal.
"You people come here from Lahore to pursue this case, but there are many people here whom you cannot see, so you better watch yourself and stay away."
