Sophie Colquhoun and Samuell Benta have been cast as troubled Ava and Donnie respectively, while Modupe Adeyeye has taken on the role of Faith, who is the younger sister of established character Mercy Chubb.
As the new series begins, viewers will see runaways Ava and Donnie descend on Albert Square after their bus crashes outside Walford. The pair soon bump into Faith, who has been kicked out by grandmother Grace Olubunmi (Ellen Thomas) after being caught getting intimate with a boy in her bedroom.
The drama begins when Ava, Donnie and Faith form an unlikely gang and search for a place to hide. However, things turn from bad to worse when the law catches up with the trio.
From left to right: Ava, Faith and Donnie
EastEnders: E20's return follows the success of the previous two series, which secured the show a prestigious Webby Award for 'Best Online Drama'.
Speaking of the new signings, EastEnders' executive producer Bryan Kirkwood commented: "The cast of E20 series three are fantastic - vibrant, exciting and talented newcomers who are set to make the next series of E20 the best yet."
E20 producer Deborah Sathe added: "Following our international award success, I am very excited to be filming our third series of E20. We have a brilliant new cast, some cracking storylines and our new E20 gang really give Walford a run for their money. E20 has come a long way since it started and I am excited about the audience watching series three!"
Young actress Eliza Newman also appears in the series as Donnie's younger sister Riley, while actor Sam Phillips is to appear as care worker Richard. Additionally, Emaa Hussen and Tosin Cole reprise their roles as series two characters Naz and Sol.
Meanwhile, former EastEnders actress Emer Kenny (Zsa Zsa Carter) returned to the E20 writing team for the new series, joined by Charlie G. Hawkins (Darren Miller), Himesh Patel (Tamwar Masood) and Arinze Kene (Connor Stanley).
Series three has been developed by BBC Learning and will address issues in the PSHE curriculum including family breakdown, bullying and teen sex.
EastEnders: E20 returns for its new 15-part series on September 20. Each 10-minute episode will transmit on the EastEnders website and on BBC Three.
> Read loads more EastEnders: E20 gossip with our guide to the new characters