My thanks to @knowtheory for pointing out that suicidal people often feel alone/apart/disconnected from other people. I struggle with this, myself.
Invite a couple of extra people to your New Year's Eve party whom you might not have thought of inviting, and you might do more good than you think.
It's also worth mentioning that being alone is perfectly fine, but when people become lonely, it's something that needs to be addressed. It's all a state of mind, after all.