I joined a growing startup (between 50-100 employees) a few months ago. Since I joined, the two other employees in my department have left and our manager has left. Main reason being they wanted more of a process and we are moving fast as a company. I actually like the job and want to make the most of it. I think there is an opportunity to grow in my leadership skills. However, I now basically have to do the work of 2-3 other people. Is it appropriate to ask for a raise? If so, how much? I am fairly compensated for the role I was hired for (base is around 150k), but my responsibilities will be expanded now.
Step 1 is ask HR and/or upper management what the plan is to replace your team. Surely somebody knows that it's infeasible to have the same rate of production with 1/4 as many people, so either they're not expecting as much from you (unlikely) or they're actively hiring (more likely).
If they are actively hiring, follow up periodically on how the hiring is going. Make sure they're actually hiring, and if they give you a timeline on when you can expect someone to join your team then follow up on that timeline. Someone will join your team to alleviate your stress.
If the company isn't replacing your teammates, then something is wrong. The company isn't producing and they are't hiring people to produce. A solvent company should never shrink in size (counting open positions in total headcount; a company should always at least be hiring at the same rate as people are leaving), and certainly should not lose an entire team's worth of people. If the company just lost an entire team and isn't replacing them, that would put me at extreme fear of the company being insolvent. To protect myself, I would be looking for a way out of this company too, so that I'm not stuck holding the bag when the company goes bankrupt.
In short: no, you should not be asking for a raise. You should be asking for more help, and you should leave the company if you don't get it.