If your friend is a Christian, he will likely need to be reminded that the Bible does not prohibit homosexuality, but rather that his sexual desires must be balanced with his biblical morals. He may also need to be reassured that his convictions about same-sex attraction are more important than his desire to march in gay pride parades and organize gay marriage rallies.
If he is not a Christian, he will need to be re-orientated to the grace of God in Jesus Christ. A gay person who is not saved will be largely convinced that Christians are anti-gay and he should assume that no one will help him. This is why it's crucial for Christians to make clear that their primary goal is to help people come to know Jesus.
You can support your LGBTQIA friends by accepting them for who they are. Oftentimes, they are longing for acceptance, especially if they have been ostracized and bullied because of their orientation. By embracing them and letting them know that their identity as a gay person is no reason to change who they are, you can provide a lifeline out of their deepest pain.
In order to best support your gay friend, you should also learn more about the struggles that LGBTQIA people experience. This will help you to avoid the common mistakes that some people make when they try to support a friend through this difficult time. In addition, you can become familiar with the nuances of LGBTQIA terminology so that you can avoid using derogatory stereotypes.