It is not valid to make a waqf of social media pages
Question

I have a twitter account, which I intended as a sadaqah jaariyah (ongoing charity) on behalf of my parents (who are both still alive). Is this kind of charity permissible, or is there anything wrong with that?
Praise be to Allah.On our website we have previously explained that sadaqah jaariyah (ongoing charity) is the waqf (endowment), which is mentioned in the hadith of Abu Hurayrah (may Allah be pleased with him), according to which the Messenger of Allah (blessings and peace of Allah be upon him) said: “When a man dies, all his good deeds come to an end except three: ongoing charity, beneficial knowledge, and a righteous son who will pray for him.” Narrated by Muslim (1631). See fatwas no. 43101 and 122361
According to Islamic sharee‘ah, the waqf must have two components: the original, tangible property and the benefit.
The one who establishes the waqf designates the original, tangible property to be “frozen” for the sake of Allah, may He be glorified and exalted, and no one has the right to sell it or dispose of it.
As for the benefit, this means spending what it produces in the manner stipulated in the waqf (endowment).
It says in al-Ikhtiyaar (3/40), which is a Hanafi book:
It means freezing the original, tangible property as the property of the one who establishes the waqf, and giving the benefit or income it produces in charity. End quote.
The Maalikis defined it as follows:
It means giving the benefit of something for the duration of its existence, which must remain the property of the giver, even if that is in a virtual sense.
End quote from Sharh Mukhtasar Khaleel by al-Kharashi (7/78).
Al-Khateeb ash-Sharbeeni (may Allah have mercy on him) said:
The waqf, in shar‘i terms, is a type of freezing wealth or property that may be benefited from whilst preserving the original, tangible property and using its benefit in a permissible way.
Ongoing charity (sadaqah jaariyah) is interpreted by the scholars as referring to the waqf, as was stated by ar-Raafa‘i, unlike other types of charity that are not ongoing; rather the one to whom the charity is given takes possession of it, both the original, tangible property and its benefits, with immediate effect. With regard to the bequest of benefits, even though this is included in the hadith, it is rare; hence it is more appropriate to interpret charity in the hadith as referring to waqfs.
End quote from Mughni al-Muhtaaj (3/522-523)
Al-Bahooti al-Hanbali (may Allah have mercy on him) said:
The waqf is when an owner who has full ownership of property allocates the benefits of his property (to charitable causes) whilst the original, tangible property remains his.
End quote from Kashshaaf al-Qinaa‘ (4/240).
Thus it is clear that dedicating an account on Facebook or Twitter or other social media does not come under the heading of a waqf. Rather it is regarded as a type of charity that brings reward so long as the benefits continue, if there is any shar‘i benefit in it for others.
It is an ongoing charity in the linguistic sense, but not in the technical shar‘i sense. That is because a subscriber to a social media website does not own the page or the account that he has; rather he is using the benefit of that account. In fact the account itself is a benefit that does not have any tangible essence. The tangible property in this case is the huge server that contains the social media websites, and these servers are owned by the company, not the account holders.
We hope that Allah, may He be glorified and exalted, will decree reward for you and your parents for all the good that is published on this webpage. What matters in such cases is to what extent there is benefit in such things, whether it is called a waqf or ongoing charity or something else altogether. What matters is that it should have beneficial content and that you seek reward for that  with Allah, may He be glorified and exalted.
And Allah knows best.