I recently had this question, with a logo for an organisation I did some work for.
Most people have no idea of the difference between vector and bitmap, and these guys were no different. I tried a number of different solutions, on-line, apps, and so on. None produced any results of any use.
So I used an online freelance service. There are a few, but I used fiverr
I asked that it was done in layers (the original had been, but none of the apps could work this out) and the result came back in a day. Under a tenner, so I gave a small tip too. Expensive for doing multiple vectorisation, I'm sure, but for a one off - perfect.