Is it appropriate to post a thank-you message on a late friend’s Facebook timeline?

I dont think we were really friends, but is sort of knew him when we were kids. I worked at McDonald's a few months ago. He came through and talked to me, and asked how my bro was doing. They were good friends as kids. I added him on Facebook shortly after that. A month ago, I had a mental breakdown in my house. The cops came, and they called the mental health place in town, and two counselors came out to check on me. He was one of them. He was so nice. He gave me his number if I needed to talk to him, and gave me a bunch of resources. He also got me a therapist really fast. One time my mom and i went to his place of work. My mom went inside and talked to the therapist to see how soon I could get a therapist. This guy comes out to my moms car im sitting in and checks in on me. I could tell he really cared. Even though I didn't know him that well, he seemed like such a kind soul. I was thinking of posted on his timeline and thanking him for helping me at my lowest point, and telling him to rest in piece. I just dont know exactly what to say.

Is it appropriate to post a thank-you message on a late friend’s Facebook timeline?
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