I can't get Angler NPC in Terraria on iOS. I think this is because I made my whole world flat and put lizhared bricks on top for armour. When the Angler was finally released on iOS I made a beach of my own and hoped the Angler NPC would come but unfortunately he didn't.
Best Answer
According to the terraria gamepedia, the Angler will spawn at random and he is not guaranteed to spawn on either ocean immediately. You may have to simply wait for him to spawn.
Also, since he is a Town NPC a suitable 'house' is required in order for the Angler to appear. If you do not have an empty house built, the Angler will not appear. Ever.
A proper ocean biome must also be present for the Angler to arrive. If you don't have an ocean or have obstructed yours you can build an artificial ocean out of sand and water. If the 'Ocean' music is playing and the background is a vast sea of water with a green hill or two than the Ocean biome is present. If not, than you may have made a mistake.