For those that are not as interested in the combat or the rest of your guild is offline and you're wanting to do some questing in the Night Market, this build is for you.
It leverages vampire stage four with three sets in particular: Coward's Gear, Prisoner's Rags, and Stormweaver's Cavort.



Coward's gear comes from battleground rewards but can also be purchased from guild traders. Prisoner's rags can be found in Coldharbour as well as guild traders. Finally
Stormweaver's Cavort is a mythic that was released with Galen and the leads generally require a bit of luck to find but the most difficult content is a world boss and lava vents which you may need to do without a lot of help if you don't have the mythic already. (Lead locations shown in link)
The reason stage 4 vampire is important is because of the final passive, Unnatural Movement:

So here's how it works: by sprinting for 3 seconds as a stage 4 vampire, we enter stealth and remain in stealth so long as we continue to sprint. Coward's gear gives us major expedition (+30% speed) and major protection (-10% damage) while sprinting. At the same time Prisoner's Rags is giving us 1000 magicka recovery as we sprint. And the cherry on top is Stormweaver's Cavort which now makes sprinting cost magicka -- in addition to a host of other core abilities.
Class is not important, but I would suggest having the Assassination skill line so we can slot Concealed Weapon on one of our bars which will give us minor expedition (+15% speed) just for having on the bar. Resolving Vigor is also very useful just to top off our health as we invariably stumble into wrong areas or get into trouble when we stop at quest markers. Dodge roll is also our friend but no need to overdo it. Side note: stage four vamps do not recover health on their own so a self heal like vigor is vital.
Combining all of this together we can sprint very quickly while being hidden from NPCs and navigate our way through the market.
Which armor is slotted where does not impact the build greatly as both light and medium armor have passives that buff sprint -- medium is a little more helpful for what it is worth. As far as CP goes, in the red tree we have Celerity to boost our base speed, and in the green tree we have Steed's Blessing which buffs our speed so long as we don't get in combat. Is that even necessary? Likely we're at or near speed cap already so probably not too important to be concerned with. There's refreshing stride in the red tree but I think neither the mag or health recovery applies due to stage 4 vamp and stormweaver's cavort.
Build screenshot:

Swift jewelry may actually be overkill, I didn't do the math on that, so maybe just go infused or bloodthirsty instead if you stumble upon a group of players and decide to help them.
Race doesn't really matter either. Wood elves get a speed buff but again, may not even be needed
Additionally I have a video that outlines most or all of the above, as well as a short demonstration of the build in action as I complete one of the Night Market quests. Hopefully this helps.
And use the group finder to find groups.
https://youtu.be/RcCC9Qp7pBg