This is the most useful review article I've found (for U.S. law), though it's from 2014: "Death By Bullying: A Comparative Culpability Proposal",
https://digitalcommons.pace.edu/cgi/viewcontent.cgi?article=...The overall conclusion I get from it is that homicide or manslaughter charges could be brought in principle, but prosecutions are rare, and successful ones even more rare. The article author proposes a legal standard for culpability, but it's not clear it's been adopted by any courts. There are also some examples of lesser charges, like harassment or stalking, but they're also rare. In addition, several states have passed specific criminal bullying and/or cyberbullying laws that might allow easier conviction on a lesser charge, but they haven't been widely tested yet.