All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
You should continue to advise your friends who do not pray, and never give up. Ask Allaah The Almighty to guide them. Give them gifts of booklets and cassette tapes on the importance of the prayer and other subjects, so that they would fear Allaah The Almighty and know that they will be reckoned by Him on the Last Day. Invite them to attend religious classes and take them to visit righteous people. There are many ways to serve the purpose of inviting them to obey Allaah The Almighty. Try your best but remember that it is only Allaah The Almighty Who guides people. However, do not keep their company unless you are advising them, lest your faith gets weakened.
Allaah Knows best.