Introverts and extroverts have different needs. I see it as more of a continuum than an either/or.
You support an extrovert by talking and being with them. They tend to recharge their batteries by being around people.
You support an introvert by allowing him time to process to think things through and to be by themselves.
When their batteries are recharged you can supports through similar ways as with an extrovert. When their batteries are low introverts need time alone.
That is considered supportive.