“My friend has drifted from the Church because others make fun of it. What should I do?” Liahona, January 2016, 61
The best things to do in that situation are: (1) be kind, loving, and accepting of your friend and (2) never waver in your testimony.
If you do these things, your friend will hopefully feel your love and acceptance and want to be around you. Also, he’ll hopefully see that ridicule and mockery are ugly things and that anyone worthy of his admiration and friendship wouldn’t attack another person’s beliefs in that way.
Your example can be one of the best things your friend can have. Be like those people from Lehi’s dream who partook of the fruit of the tree of life and were mocked by those in the great and spacious building but “heeded them not” (1 Nephi 8:33). If your friend sees you upholding your beliefs and standing up to others’ mockery with dignity, respect, and good humor, he may see that it’s possible for him to do the same. If there’s still a seed of testimony in his heart, the example you set and the testimony you bear may be some of the things that help him feel the Spirit and remember what he once knew.