The Muslims should cooperate in sighting the moon and informing the authorities
Question

What should a person do if he saw the new moon of Ramadan or Dhu’l-Hijjah, and he did not tell the relevant authorities about that?.
Praise be to Allah.What the one who sees the new moon on the night of the thirtieth of Sha’baan or the thirtieth of Ramadan or the thirtieth of Shawwaal or the thirtieth of Dhu’l-Qa’dah should do is to inform the court in his city, unless he knows that the sighting of the new moon has been confirmed by someone else, in accordance with the words of Allah (interpretation of the meaning): 
“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety)”
[al-Maa’idah 5:2] 
“So keep your duty to Allah and fear Him as much as you can; listen and obey”
[al-Taghaabun 64:16]
And the Prophet (peace and blessings of Allah be upon him) said: “The Muslim must hear and obey.” Narrated by Muslim (1839). 
And he said: “I urge you to fear Allah and to hear and obey, even if a slave is appointed over you.”  
It is well known that the ruler via the highest judiciary council of Muslims requires the one who sights the new moon to inform the authorities. The Prophet (peace and blessings of Allah be upon him) said: “Fast when you see it (i.e. the new moon) and stop fasting when you see it, … but if it is too cloudy then complete the number.” There is no way of following these ahaadeeth except by the help of Allah, then by cooperation among the Muslims in sighting the new moon, and informing the authorities when it is sighted. The one who sights it has to inform the official authorities of that. Thus obedience to the shar’i commands and cooperation in righteousness and piety will be achieved. And Allah is the Source of strength. End quote. 
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him)