Maokai is supposed to be a tank and mage, but he can also work well as a supporter.

Here his negatives and positives:

negatives:

-must get near the enemy
-not so tanky like other champs

positives:

-good killsaver
-infinity wards (E)
-relic shield works very well with passive
-good CC

With your Q W combo, you can get your ADC an easy kill.

The best part about Maokai support is that he can use his E as wards and as poke.