If you are reading this, you may be in a position where another E2 staffer, or, more likely, a user, is expressing suicidal ideation or struggling with other kinds of self-harm. You may have been alerted by something in the chatbox, a daylog, or elsewhere.
The important thing for you right now is to not panic, and to follow appropriate (and limited) steps to help that person.
Your ability to help will be limited by the amount and type of specialized training that you have. For most people, this is little to none. There's nothing wrong with that, and there are still things you can do to assist a person going through issues involving suicide and self harm.
Don't try to "talk them out of it", or scare them into not doing it. Don't try things you've heard or seen on television, read in books or magazines, or even things you have heard from friends or family who have dealt with these issues before personally.
Intervention is a very complex and difficult thing to do correctly. Fortunately, there are many organizations devoted to helping people without the appropriate training do the right thing in exactly these kinds of difficult situations.
Below is a list of organizations offering assistance both to you, and to the person you're trying to help.
United States
If the person you are reaching out to is in the United States, you can and should follow the guidelines of the National Suicide Prevention Lifeline.
If you don't know the person very well, please refer to the NSPL Guidelines for Helping Someone Online.
If you do know the person well, whether from real life interactions or just a sustained relationship online, you may consider NSPL's Help for Someone Else.
Another US-based help line aimed specifically at LGBTQ/Questioning Youth is The Trevor Project.
United Kingdom
Help for a Friend at PAPYRUS
Samaritans.org - If you're worried about someone else
Elsewhere
Wikipedia maintains an international list of suicide crisis lines.