You first meet Zevlor in Act 1 of Baldur's Gate 3. He's the Tiefling leader you speak to after the goblin attack at Emerald Grove and he tells you that the Druids want them to move on. Assuming you choose to save the grove, Zevlor turns up again in Act 2. Well, sort of. Once you reach Last Light Inn, you'll hear that he's gone missing after his party of travelling Tieflings were attacked by Absolute soldiers.
If you've gotten this far, you should already be pretty familiar with how things work. That said, the Shadow-Cursed Lands aren't quite as friendly an area as the Wilderness and it's wise to pick up a Moon Lantern if you want to travel around with ease. If you're having no luck locating Zevlor in Baldur's Gate 3, here's where to find him.
Baldur's Gate 3 Zevlor: Where to find the Tiefling leader
Pretty much as soon as you arrive at Last Light Inn, Jaheira will tell you that Zevlor is missing. If you're anything like me, you've searched high and low through the Shadow-Cursed Lands, trying to find him but, also like me, I expect you failed. Don't worry; you won't access the area he's found in until you're ready to progress the story.
After you've made the Nightsong choice and fought Ketheric Thorm on top of the Moonrise Tower, you'll be able to descend into the Mind Flayer Colony hidden beneath. This is where you'll find Zevlor in the Tadpoling Center, encased within one of the many pods, waiting to be turned into a Mind Flayer.
Interact with the console by the door to free him, though be warned that doing so will mean a fight against Mind Flayers and Intellect Devourers if you want to get out alive. Luckily, though, Zevlor and the other soldiers you free will help you against them. While you're in the area, be sure to check out the Necrotic Lab, too, if you want to read some brains with the Mind Archive machine or try your hand at the brain puzzle.
Once you manage to get away, you can speak to Zevlor, who will then explain what happened to him and the events that led to his capture. Now you just need to find Mol, huh?