If you have done all this and you have a friend who has admitted to having depression, I encourage you to follow the advice on this page and be a friend. However, if your friend is struggling and you truly believe an intervention is necessary, there are a few final words of advice in the form of a mock-intervention that you may find helpful in planning an appropriate intervention, taken and adapted from Active Minds.
Pick the right setting: Choose a private place where you both feel safe, but prioritize the comfort of your friend so you are on equal footing in that space. Also, pick a time that is flexible so that you don't have to end the conversation early.
Avoid an ambush: Approach your friend one-on-one to prevent your friend from feeling overwhelmed or attacked, though having support from a friend's parent (if they are on good terms) or a professional may be helpful.
Be prepared with resources: Know how to contact local or online mental health services so that you can help them with their first appointment, should they want it.
Take care: Know that your friend may not react pleasantly but that you are doing the right thing; their reaction is not about you, so have your own social support so you ensure to look after your own physical and mental health.
Have some questions prepared to start the conversation: Some examples include, "I've noticed that you haven't been acting like yourself lately. I'm worried about you, is something going on?; What can I do to help?; Have you spoken with anyone else about all of this?; Are you getting the care you need?; Do you want me to walk with you to the counseling center?; What do you feel like? What are you experiencing?; Have you ever had thoughts about hurting yourself?"
Finally, formulate "I" statements: These are helpful in approaching such a delicate topic because they help communicate concern without appearing judgmental, and they encourage both conversation and problem solving. Consider using the following approach: "I feel [emotion] when [situation] because [why]. I'm wondering [suggestion]." For example, "I feel concerned when you can't get out of bed because I care about you. I'm wondering if it would help to talk to a counselor."
With this plan in mind, you can begin formulating how you want to approach your friend. Best of luck in being the friend!