How to do a select with multiple results in a single row

Even though you create an SQL for this, it will cost you a lot of processing, as you will have to break this string id_users into a list, and make a JOIN on it.

What I suggest is that you redo your structure, using the way most systems work in this situation. This way:

TABLE messages:

id INT PRIMARY KEY,
title 'titulo da mensagem',
text 'texto da mensagem',

TAB users:

id INT PRIMARY KEY,
name 'nome do usuario',

users_messages:

id INT PRIMARY KEY
id_user (FK)
id_mensagem (FK)

It is a super basic Many-to-Many structure, meaning a message can belong to 1 or more users, and a user can have 1 or more messages. With this, your query looks like this:

SELECT u.id, u.name, m.id
    FROM users u
    JOIN users_mensagens um ON um.id_users = u.'id'
    JOIN mensagens m ON m.id = um.id_mensagens;

A friend (@rodrigoborth) helped me by talking about 'FIND_IN_SET', which made me arrive at the following query:

SELECT mensagens.id, users.name, mensagens.title, mensagens.date
    FROM mensagens INNER JOIN users
        WHERE FIND_IN_SET( users.id , mensagens.id_users ) ORDER BY mensagens.id

Simplifying my problem and so temporarily answering the question! =)

Your database seems denormalized, I advise if possible, creating a table to relate the user to the message. But it follows an option by using a subquery to bring users related to the message, reducing the number of query result rows.

SELECT
m.title,
m.text,
m.id_users,
(
  SELECT 
  GROUP_CONCAT(u.name SEPARATOR ';')
  FROM users u 
  WHERE FIND_IN_SET(u.id,m.id_users)
) as nomes
FROM mensagens m

In this case the query returns the users related to the message in the format usuario1;usuário2

Example: SQLFiddle