I'm sorry to hear about what your son might've been at risk for, and I completely understand how you feel that you should be monitoring his online activity.
As is already said in the topic Cheza posted, a furry "lifestyle" (I'm enquoting this because I believe being a furry is more of a hobby than a lifestyle to most people), or their activities consist mostly of socializing with others in the culture, sharing, and sometimes also making art and literature.
Furries do occasionally meet up in conventions, but those are almost always official events with many people attending them, and security present. So those would be a very silly place for predaters to try their luck at, I guess.
As for the negative parts of the lifestyles, there's no way of getting around it but it's just considered as a bit of weird thing, and people can try use that against you, often by ways of shaming, if they so please.
I've personally found that it's really not too bad, though. There's no need to declare being a furry at any given oppertunity, so most people only find out that I'm a furry once they're atleast somewhat befriended with me and already have a solid impression of who I am, and although they may sometimes demand a bit of an explanation because it's occasionally a bit of a controversy, once I've talked about what it means to me they're always okay with it.
And if your son is someone like me, with a decent amount of self-confidence, then that shaming thing is an innefective method, as being a furry just isn't a bad thing that one should feel ashamed for.
My older brother, for example, has tried to use it against me a couple of times, but because I just shrug it off since there's nothing wrong with being a furry there's just nothing he can do with it.
As for advice on encouragement, and whether you should speak to him about it:
I do believe that it would be very nice for your son if you were to just tell him that you are aware of his interest and that it may be a bit of a weird thing, but that it's not a bad thing, that you accept it and that he shouldn't have to feel ashamed about it.
My own father, when I admitted to being a furry, said something among the lines of "And some people go to a stone building every sunday to pray to a man hung on a cross over two centuries ago. People are weird, it's what they do, but I'm just happy your past-time isn't something like gambling, or being junkie." And it was just nice to hear for me that it didn't influence how he thought of me.
Fathers are quite influential figures that children often look up to, so I'm sure it'll just be nice for your son to hear that you still support him, and that he don't have to feel ashamed or hide it.
If you want to give a bit of encouragement to your son, I would suggest looking mostly towards helping him with self-confidence, and encouraging him to find a community of other furries, and just in general to socialize. (Because people are better together)
But, your son may wish to do this on his own, so if you feel that he doesn't want or need much encouragement, there's no need to push. He'll find his way around.
Lastly, a couple of things of notice.
The word "furry" is a very wide-encompassing term. There are a lot of diffirent sub-cultures within it, all with diffirent interests and standpoints, and as John said, there deffinetly may be bad apples between those.
But, that really does not neccecarily mean that your son is one of those bad apples, or is being influenced by them.
And, for some reason, a thing that losts of people that dislike furries tend to use is the notion that they are into bestiality.
This is simply not the case. As we've mentioned, sadly there are bad apples, and this case is especially a rare one, but as a whole furries do not partake in and do not support this!
That'll be all from me, I guess. I hope I've been helpfull!