Since the introduction of housing to ESO a bit more than a year ago, a lot of RP shifted inside those private places.
Yet still one can encounter RP at open spots. For Stormhaven RP
this is usually the Cloudy Dregs Inn in Wayrest. For other OOC hub guilds
I cannot tell unfortunately.
Be aware of ESO splitting up the world into multiple instances/shards/phases (however you prefer to call it). This means the same place might be divided into two for technical reasons. That leads often to people being in the right place, yet not seeing any other RPers. They then usually are in another phase. A mirror-world so to speak. OOC Hub Guilds are mainly there to be able to teleport via Travel to Player to those in the right phase and then be able to RP with them.