Urge your school administration to help you help your students by establishing an anti-discrimination policy or by explicitly including LGBT people in their existing anti-discrimination policies.
Your students take your lead, especially at impressionable teen ages. Their view of the world is still developing and can often be wrongly influenced if they aren't shown other alternatives. You, as their teacher, play an important role in molding these teens for the future. How you speak of, portray or act towards lesbian, gay, bisexual or transgender people can have a lasting impact on your students' view of LGBT people and LGBT issues.
Their view of LGBT people directly relates to how they interact with other teens that happen to be LGBT. Some teens attack (either through words or violence) what they don't understand or perceive as different or weak, creating unsafe condition for those that are considered outsiders.
You can help create a safer school environment by educating all students and increasing their positive awareness of LGBT people and diversity. Set the tone, dispel gay stereotypes, have little tolerance for jokes or comments, and show your support for LGBT students through an open door policy and sponsored programs.
Acceptance and diversity is an ongoing process and it takes the commendable efforts of committed individuals such as yourself to help create a more inclusive environment for LGBT teens and all people.