First, a little bit of background:
I've been in this company for a little over 2 years. We were a small team of 3 people managing and developing the tools for our companies (we are the HQ). Almost 5 months ago, one of our colleagues left and since then I am having an increased number of tasks. Over these 2 years I have learned a lot and now I'm faster and more efficient at completing tasks and am able to tackle more complex matters too.
This job was advertised as "the minimum salary for this job is xx$". And since before this job I've done a one year internship and it was the first "real" job plus the fact that it was matching perfectly with what I've done for one year and it also was what I wanted to continue with, I didn't try to negotiate this minimum offered salary out of fear of not getting the job. Fast forward 1 year later, I was waiting for the first employee appraisal in the hopes that I will be able to get a salary increase. Unfortunately, the management decided they want to change the direction in which the company is going and my boss was let go. Shortly after, we got a new boss and nobody had his appraisal that year from the department. Waited almost another year for the next appraisal, for which I have asked multiple times, over a time span of 2 months, and finally had the meeting and at the end of the meeting finally asked for a raise.
Off-topic: The raise mentioned above is quite big in %, almost 30% but considering that even with that raise for my current experience I will be on par with the job market or even lower. I am not justifying my asked increase based on the fact that I've been doing this for over 2 years, but based on the market and what they would need to spend to replace me. I'd like to point out that I received a positive feedback in the appraisal and was told to keep up the good work.
Back to the salary negotiation
I didn't get a no from my boss for my asked raise, just that he needs to talk to HR. I was pretty happy back then because I thought that even if in the event in which I wasn't to going to get exactly what I asked for, I would be happy with even a slightly lower increase (20-25%). Now 3 months and a half passed and I have asked 4 times about the status of my request and stating that this is important to me not only due to the financial part but this would reflect how the company values me. Every time, I get more or less the same answer: still waiting for an answer from HR (my boss has a very important position in the company and probably he is not being honest as this salary increase should be very well in his power).
This question is not about the %. As mentioned before, I didn't get a "no" for one second or a remark that it's too much.
I love working here and I have spend a lot of time to learn the specifics of this company, I would like to do everything in my power to avoid leaving.
The company is looking for months for someone to replace the colleague who left and they haven't been able to do it so far (mostly because with the set of skills asked, those people are already working as consultants and earning more). Note: the colleague which left the company, left for the same reason: asked for a raise and he got a "no". But at least he got an answer pretty fast...
How should I continue from here? Should I try to be more pushy and ask again if he's (boss) happy with my performance and if the answer is "yes" then go ahead and ask firmly to have my situation finalized. Is it normal that it takes this long for an answer, or this would show a complete lack of interest for the employee? My goal is to at least get a "no" or a "yes", tired of waiting.
Edit: Probably not a duplicate of "How to approach my boss if I'm feeling underpaid". I have already read that even before I had my first negotiation and followed the advices there to discus about my achievements and why I should I be getting a raise. Now it's a matter of done that and now what?
Edit nr. 2: Since I can't add a comment to Joe's answer due to the low reputation, I'll type additional info here. First of all, thank you Joe, long time reader of your answers here. My boss talked to HR for sure at least once, because there was also the discussion if they should change my contract type to have more hours included, to that HR sent back quite fast a "no" because I am not above a certain trigger that they are having. I know that they can't afford losing another team member because due to the specifics of the job, it takes 6 months to 1 year to get familiarized with all the custom tools and how they are built (can be faster for a fast learner). Now, I don't know why would HR drag this, the only reason I could think of, is they are first looking for a replacement for my colleague and once they have that they will say "no" to me.