Followed and grabbed by coworker

I began working at a health tech startup in SF and the company culture was pretty bad. My story is just one example of this. This employee was one of the first employees at the company, and was high-up in the engineering team. He was beloved by everyone, and was super social -- he made an effort to get to know everyone as the company grew quite rapidly. We had a conversation every now and then, but were not particularly close. One day he brought in his adorable tiny dog, and so the next day when I saw him, I looked down at his feet and made a sad face, saying "where's your dog?" A few weeks later, when I ran into him again I joked around that he was still witholding his sweet dog from all of us, and he loudly said "[My name] always looks down there and then looks disappointed. I think she's not impressed with what I'm packing." Not only was this incredibly inappropriate, he repeated the joke often. I decided to let it go, and just shrugged it off as strange behavior. Our next major interaction was during the company holiday party. When I arrived, he was already quite drunk. He kept talking with me, and everything was cordial. I noticed throughout the evening that he seemed to be following me, showing up no matter where in the crowded building I was with my co-workers. At one point we were chatting and I asked where his wife was--as every other department head had brought their significant other. He said that she was shy, and didn't typically like events like these so she was home with their young children. After this happened, I went to dance with some friends, and then he came up behind me, putting both of his hands on my waist and pulling me close to him. He started squeezing my hips and whispered, "is it okay if I tell you how good you look tonight?" I could feel his hands start to move south, and I turned around and said "Absolutely not. You better leave me alone." He looked shocked, and stumbled away. The next week I told a few co-workers about the incident, and one told me that she thinks his marriage is troubled and that he's probably just lonely -- I had “no reason to be upset.” Multiple other co-workers told me about men that groped them at that party, tried to kiss them, and one even told me that a manager in my department followed her when she went to lay down after drinking too much and she woke up to him touching her legs. One told me she didn't want to go to HR because she was up for a promotion, and didn't want to rock the boat. After hearing all this I decided to take this incident to HR. I felt supported by the HR department, who validated that his behavior was not acceptable and that she would chat with this employee. She said she would follow up with me after. Two weeks later there was no follow up, and when I reached out to her she said that he was "embarrassed." Interestingly enough, he left the company not too long after that. #metoo