Yes they can be attracted to a depressed person because that person is pulling them towards themselves with their state of mind. They can sense the chink and latch on. What needs to be done is the chinks need to be armoured up so there is nothing to hold onto, even if it is totally fake it until you make it, it does help.

Will post more when I get home from work tonight. I'll pull a couple of books out and post some info.