This is a term being used in the last few years to describe a personality type that has always existed. You could also refer to such people as being negative (in the sense of not offering anything positive, not just seeing the downside of everything) or I've even seen them referred to as emotional vampires. This seems a bit harsh - so does the word toxic - but there's no denying that, sadly, you do meet people who seem almost fo poison the air around them, making it hard for others to function and depriving them of energy.
This article gives some clear descriptions - again a bit harsh, but I must admit I recognize the types described here and maybe you will too.
The typical signs are that a person expects everything from others while giving very little, always blames others and won't take responsibility for their own life. They are often very unhappy people, but it's hard to know how, or whether, to help them.