Is it permissible to collect donations and advertise them on social media for the purpose of carrying out an ongoing charity (Sadaqah Jariyah) on behalf of a deceased person, such as building a mosque?

There is no objection to advertising and collecting donations on websites, as this is a way of pointing to good, for the Prophet, peace and blessings be upon him, said: "Whoever points to good will have a reward like that of its doer." Those in charge of the website must secure it to protect donors.