This is not an instance where magick is at all needed. The best course of action is for the person in question to draw strength from within. You may wish to comfort the person, but this battle is only to be won within the depressed person.
Perhaps if someone identified the source and cause of the depression and take steps to influence or stop the 'negative' influence then a solution or relief can be found. If there is an outside influence affecting the depressed person, try removing the outside influence.
If you are dead-set on using a spell or something, the best thing for you to do would be to 'send' helping energies to the depressed person. This will help if you believe it will.