I don't understand people saying you can't play her support. You can take almost any champion as support with some thought and preparation. That being said, you don't take them to a different position and then play/build them the same. You need to adjust to your position's needs.
I love playing as
and was S ranking her as support all season 7. This post inspired me to try her with the new rune system and I built something that I think is extremely fun to play.
The goal in my build (and from experience of playing supp liss) was this: surviving dives, slow/poke, and lane sustain
Keeping in mind that her abilities carry a lot of power on their own, your job as support isn't damage, and games are much shorter now than they used to be...
RUNES:
Aftershock, Font of Life, Conditioning, Second Wind
Nullifying Orb, Scorch
ITEMS:
early

core

and
or
depending on enemies
you want both
and
, but path your build depending on the enemy team's comp.
SUMMONER SPELLS:

ABILITIES:
Max your Q first. This is your main poke/slow. With FoL it's going to heal your adc, and at lvl 1 it does 90 damage with Scorch.
I like to get 2 points on both W & E, then max E... But follow your heart on this one.
As for your R... I use it on myself when in a team fight, but if you're soloing out one target for a kill (i.e. their adc is caught out of position) then I'll tag them with it instead or use it as a kill shot early on.
Liss is great for shutting down heavy damage dealers and take them out of fights.
You will definitely tilt a teams carry when you E/W combo them with AfterShock, use
and
, plus Nullifying Orb triggering, and on top of that your R.
They might even stop trying to kill you. (jk they will want you dead more than a swarm of killer bees).
Anyway... I'm having a lot of fun with this build.
If you think of anything that might help it out or what a good 6th item would be, let me know.
[slayer-pantheon-thumbs]