Chained Echoes

There are 23 total recruits, which you can find starting in Act 2 after your clan is created.

Act 2

1. Falora - Hermit’s Isle
Sells hints on other recruits for 1000a (unnecessary with this guide!).
You can find her directly south of the Hermit Isle crystal.

2. Guy - New Wyrnshire
No rewards.
After you get the airship, head to New Wyrnshire, just north of Hermit's Isle. Go straight forward into the inn and head upstairs. Exit to the rooftops and head around to the left and up. There's an easy-to-miss metal beams that you can cross and follow around to some rooftop merchants. Guy will be to the right of them.

3. Deimsch - Farnsport
Sets up a smithy in Hermit's Isle.
The blacksmith from the blacksmith tutorial at the beginning of the game. From the Farnsport crystal, head right and then to the top left of the map.

4. Bernd - Rockbottom
Once you reach Clan Rank 4, he'll clear a path to a chest in Hermit's Isle.
From the Rockbottom Crystal, head right and up the stairs. Head into the house on the left (do not cross the bridge). Watch an amusing scene between Bernd and His "Not?!? Wife"

5. Bao - Mount Rydell
Grants a 50% chance to gain additional SP when defeating enemies.
In the airship, simply travel to Mt. Rydell and land. He's right there.

6. Pignon - Flower Fields Of Perpetua
Eventually opens up an onsen (hot spring bath) in Hermit's Isle at Clan Rank 4.
With the airship, travel to the Flower Fields of Perpetua and head north towards the Leviathan's Trench entrance. You'll get a cutscene in one of the forested areas with Pignon joining up.

7. Gormit - The Hooge
No rewards.
After you complete the side quest "The Food, the Chap, and the Hungry" (getting Tomke into your party), you can find Gormit back on the Hooge. Head around to the top right of the map and wait for a moving platform to show up. Jump on it and go into a new area, and then follow the path to the bottom right. There will be scene where Gormit joins up.

8. Tehlla - Arkant Archipelago
Adds information on where items can be found: press on the Loot tab, or in the Blacksmith view to see where each upgrade material can be found.
Head to Arkant Archipelago and go left to the next screen. Tellah will be standing there in white robes.

9. Pavel - World Map
Fishes up random rewards from a pier in Hermit's Isle (head the left entry cave, then to the first cave on the right, and then exit down to the pier). You get one item per hour of game time, and it stacks (eg: after 5 hours, you get 5 items).
You can find him in the far southwest of the map while flying around in the airship. Land on his raft and speak to him.

10. Vesta - World Map
Adds a display to the bottom left of the screen that shows how many chests are left in the current map area, as well as indicators for whether there are any hidden caves or buried treasures.
In the airship, fly west of Arkant Archipelago (southeast of Rockbottom) and you'll see an island in a lake. Land there and talk to Vesta.

11. Eddie - World Map
Lets you choose what music to play on Hermit's Isle once you reach Clan Rank 3.
In your airship, you can find another airship flying around erratically on the western side of the map. Catch up to it and land and you'll get a scene with Eddie joining up.

-----

With everyone above and you should have enough recruits to get to Clan Rank 2, which is required for some of the Act 3 recruits to show up.

Act 3

12. Archy - Shambala (Clan Rank 2)
No rewards.
After you destroy the ASACs in Shambala and can fly in your Sky Armors, head to the bottom left map section. Archy will be on the lower part of the island with the Leonar Statue (Chemist Class Emblem) on it.

13. Thopas - Shambala
Grants an extra crystal from crystal sources for a total of 3 chances.
He can be found in the northeastern section of the Shambala map on an island with 3 crystal sources. Wait until you talk to him to mine the crystals.

14. Triony - Farnsport
Triony will join Pavel on the fishing pier, and will eventually fish up a special item once you reach Clan Rank 4.
He's located in the docks area in the southeastern section of the Farnsport map. Follow the docks, and you'll see him sitting on the edge of a wharf in the middle of the area.

15. Kayn Sivar - Farnsport
Allows you to buy cosmetic appearances for your airship on the Hooge.
Kayn is just northwest of the Farnsport crystal. Just walk up for a scene and he'll join up.

16. Bob - Tormund City
No rewards.
Head to Tormund and go to the west screen with the park area. Bob will be sitting on a bench in the middle of the area. Talk to him and choose "Sure" when prompted and he'll join up. If you don't, it may be possible to speak to him again and try a second time to choose the obviously correct dialog, but you can always reload a save as well.

17. Linus - Tormund Underground
Joins Eddie on stage at Hermit's Isle and will play random sound effects when interacted with.
Head to Tormun and go to the underground market area. There will be a dog running around the middle area. Catch him to "recruit" him.

18. Murchand - Flandern
Sets up shop at Hermit's Isle allowing you to buy consumable items there.
From the Flandern crystal, head directly west to find a hammerhead shark looking character hiding in some tall grass. Talk to them and suggest they need a change of venue to get them to join up.

-----

With everyone above and you should have enough recruits to get to Clan Rank 3, which is required for some of the Act 4 recruits to show up.

Act 4

19. Gimaj - Ograne Grottos (Clank Rank 3)
Grants a 50% chance to get 5 additional SP after battles.
Grimaj can be found after completing the "Chained Echoes" main storyline mission at the beginning of Act 4. You can find him in Ograne Grottos, in the area west of the area with the central travel crystal. You may run into Tadeyes, which require Incocybin berries (purchasable from the Goblin town if you've completed the side quest "A Goblin's Dilemma"). You can also run back and forth between the two areas until the Tadeyes disappear, which means a unique Tadeye monster has spawned out of the way on the far left side. Go down and to the left, cross two bridges, then head immediately up to find a climbable wall you can descend to a waterfall. Grimaj will be in the waterfall and will join up a short conversation.

20. Zellor - Flower Fields of Perpetua
Grants a discount in all shops.
Zellor is at the research camp in the bottom righthand desert area of the Flower Fields of Perpetua. In your Sky Armor, head to the far right and then follow the wall up to a camp of scientists (diagonally down and left from the top right corner of the area). Zellor will be standing in front, jumping up and waving his arms. Speak to him to have him join up.

21. Bernd’s Wife - Rockbottom
She allows you to select what category of crystal (Status, Offensive, Defensive, or Utility) to get from crystal sources.
Go back to Bernd's house and chat with his "Not?!? Wife". She'll head to Hermit's Isle, so go back there and head to Bernd. You'll find her giving him a hard time, after which she'll join up. You can find her in the inn, which is the top building to the left of the travel crystal.

22. Jack - Fiorwoods
From the travel crystal at the top of the bottom left area of Fiorwoods, go down and around the small lake to find the research camp. Jack will be standing just above the camp in an area he's just cleared of trees.

23. Fridolyn - Vacation Island, World Map (Clank Rank 3)
No rewards.
Fridolyn can be found as part of the quest "A Little Vacation". After you've found and beaten the sentient vegetables in Basil, you'll be able to find a small manor house you can visit in your airship. It's located just northeast of Arkant Archipelago. Fridolyn will be there with some talking pigs and vegetables and will offer a side quest. Fulfill the quest, and he'll move to Vacation Island, which is located on the island with a mountain just southeast of Arkant. Once you reach Clan Rank 3, you can visit him at Vacation Island (up and to the right, napping on his pig) and he'll join your clan.

-----

Once you get all recruits, the achievement will take a moment to pop. For me, Fridolyn was the last recruit and I had to press to exit to the airship before the cheevo popped. I almost reloaded the game because it took so long!