First of all, social demands have very little bearing on introverts. Although your case could be made accurately for naturally social individuals (e.g. extroverts), for introverts the situation gets a little more complicated.

Introverts can become depressed by factors that seem out of their control. If they repeatedly try to detatch themselves from these factors and attain some sense of freedom from them, but are repeatedly denied such by their environment (their friends, their family, their work, etc.) then they may lose hope. Loss of hope appears to be the deepest cause of suicide, because why go on to the next day when you know already that you will have not have a chance then at fulfilling your dreams? Psychotic influences (pathological friends and family) and drugs go a long way to making one feel they should hold out no hope for the future.

The best way to diminish the likelyhood of suicide in people you know is to encourage them to take heart for tomorrow, even if there is no reason for it. Reasons have a way, in our random world, of presenting themselves seemingly from nothing. It's impossible for us to know everything, so why not look at the glass as half-full, as opposed to half-empty?