"I'm really pleased to be staying on at the Dragons," said Evans. "I've been very happy here and I feel that we are moving forward. I know we had a few tough results over the Christmas period but we know what we need to do and are ready to put in the hard work to get back on track for the rest of the season.
"With the planned new training facilities and the team spirit here, the Dragons are moving forwards and I want to be a part of that."
Brew, who joined the region last season, is also keen to be a part of the future being built at Rodney Parade.
"I've really enjoyed my time at Rodney Parade since last season," he said. "I feel this region and this team are going somewhere. I've developed as a player here and the team has a bright future."
Dragons Rugby Manager Robert Beale has expressed his delight at the signings.
"We are delighted to have retained the services of all four players. It forms a key part of our ongoing development policy and these four players have been provided with opportunities and have readily made the most of them.
"I'm delighted that Wayne has signed this two-year contract extension. He has proven over and over his value to the region. This contract is a well-earned reward for his hard work and we are looking forward to him getting back on the pitch to continue his career development.
"Martyn Thomas is an exciting young talent and this contract shows that we have faith in him to fulfill his potential with the region and become a regular member of the regional side.
"I'm really pleased to have reached agreement with Aled. He is one of the more consistent players this season and his return to the Dragons has kick-started his career again - allowing him to show some quality form. Aled knows what he needs to work on but he is one of a few players who have the dynamism and energy to change a game in our favour and we are very pleased to have secured him at Rodney Parade.
"I am genuinely thrilled for Tom Riley. Having worked alongside Tom seven years ago as an under 18 player, I am well aware of his abilities. He was presented with an opportunity at the start of the season which he has grasped with both hands and very much deserves this contract - not only for his playing abilities but also for his work ethic and professional attitude on and off the pitch which are outstanding."