It is possible to organize prayers collectively just like individual, that is by organizing gatherings in remembrance of Imam (peace be upon him). Such gatherings in addition to the prayer we offered for the Imam (peace be upon him) there are other good things that is included, like reviving the issues of the Imams and mentioning their traditions (peace be upon them) and so on.
The writer of Al-Mikyal (may Allah raises his position) includes organizing gatherings in remembrance of the Imam among the duties of the creatures during the occultation of Imam (may our soul be sacrificed for him) mentioning during the gathering his virtues, merits, praying for him and spending our lives and money in this respect because that is among propagation of Islam, announcing the words of God, assisting good and faith, glorifying the signs of God and helping the friends of God.
CAUTION: Sometime such gathering may become compulsory if such gathering can serve as an avenue to bring back to guidance and right path those that are exposed to deviation and straying from the right path, base on the law of enjoining people to good and abstaining them from bad (Amr bil Ma’ruf wa Nahyi anil Munkar) like wise the law of guiding an astray person and abstaining people from innovation. Allah the Most High is the Protector in all condition.
 – Mikyalil Makarim 2: 169.