They may try to put you off. Stay in touch. Invite them to do things with you. Don't force them to be cheerful. Stick with them.
Offer help early.
Offering to help early on may prevent the teenager from sinking into a deeper depression. Help to understand the cause of distress. Understanding the source of distress is one of the best means of freeing ourselves from its effects. If you are trying to communicate or support a depressed youth, don't be surprised if the responses you get are irritable and negative. Don't take them personally.