Sympathizer (noun)

A person who supports or feels compassion for a particular cause or group.

Origin:

From the late 17th century, from french sympathisant, from the verb sympathiser, from ancient greek συμπαθέω (sumpathéō, "i am affected with the same feelings as another"), from σύν (sún, "with") + πάθος (páthos, "feelin.g")

Examples:

1. He was a sympathizer of the rebel group and often gave them money.
2. She was a sympathizer of the feminist movement and often attended rallies.
3. Many people who were sympathetic to the cause of civil rights in the 1960s became active sympathizers.
4. The government arrested several sympathizers of the terrorist organization.
5. He was a sympathizer of the communist party, but he never joined it.