I think if a social media organization encouraged a #highspeedometer hashtag they could also be liable. It's not the filter or the speedometer, it's that Snapchat set up a defacto social incentive for speeding.
I cannot help the feel that this "social incentive" argument is the adult cousin of "but everyone's doing it, mom!".
Even marketing would be tough to catch them on as how many grocery stores in college towns sell beer bongs right next to beer displays that are a few feet away from liquor. At what point would they be liable? Beer bong directly adjacent to bottles of JD/ shrink-wrapped with bottle/ buy 2 bottles of JD get a beer bong.