I'm Sorry to hear that has been occurring. If you have been receiving these messages in mass I don't think that is normal at all. I mean, I've been here myself, and I can say that I have not received any messages to the extent that you are. Again, I apologize. Not only for the messages that you are receiving, but for My response right now. I feel so terrible that you have to endure that, and if it were me I would be saddened, and even furious.
Blahtherapy, is not meant to host malice, and I'm sure that you know that. Nonetheless, If you haven't done anything yet, I think you should report these people. Especially, If you've told these individuals to stop and they haven't. That would go along the lines of Harassment, as they would be made aware by your warnings that what they are doing bothers you.So, If no one has listened to you, I'd definitely report them.
Also, in your settings you can limit the people who can message you. There's a Message privacy setting, which will allow you to go from public, to only friends, and from there customize. Customize allows only people that you have entered in that list to message you. Additionally, You could block these individuals if they are becoming too cumbersome.
But, I'm so sorry that you had to deal with that. I don't think well-intended or vulnerable people deserve that kind of stuff. I only hope, that with the decision you make that things will fare well for you.