Identify the missing number in the given series.
$8,24,72,?,648$

Let's determine the pattern of multiplication between successive terms:
* $8\times 3=24$
* $24\times 3=72$

The pattern is that each number is multiplied by $3$ to get the next term.
Therefore, the missing number is:

$$72\times 3=216$$

Let's cross-verify with the last term:

$$216\times 3=648$$

The logic holds perfectly.