When talking about groups of people that share some idea it's not easy to find a "true" russian suffix that suites the task. The only pre-cristian beleiver I can recall is волхв, ведун.
Other kinds were called so by Russian cristians: язычник, идолопоклонник.
There are also some cristian sects like иконоборец, старовер.
(You may also want to see a list of "magic people" that we have here).
Most other religious movements have names borrowed from Western culture, so they have Latin, Greek, French, English, etc. suffixes.
So, based on existing names of religious movements:
- Suffix -ит (каменит) is OK, because many such words were borrowed from Western culture.
- Most local names for such movements are usually based on several words made into one:
- Старовер = старый + верить: верить по-старому (believe in old way);
- Иконоборец = икона + бороть: бороться с иконами (fight against icons);
- Идолопоклонник = идол + поклоняться: поклоняться идолам (praise the idols).
If the second model looks interesting to you, then you may try to join some words to create your own like камневер (believer in stone), камнеискатель (stonesearcher), камнепоклонник (praiser of the stone), камневидец (the one who sees a stone), etc.
As for "true" russian suffixes - I think most of the meanings are already occupied, for instance Wiktionary reads that "каменец" is a person that lives in cities like Камень-на-Оби, Каменка, Камень, etc..