I am the VP of Growth of a, so the short answer is yes :). Let me give you some tips about hiring such an agency.
You can find quite a few growth hacking agencies to help you achieve your goals. However, before doing so, you need to to be determined to change your mindset. For example, do you really know what your goals are, or should be? Are you ready to split your time 50-50 between product development and getting traction? Do you have at least one person in your team really committed to growth?
mentioned a great article, and you should check it out thoroughly. However, if you really want to grow, and not just gather some emails massively, or see some spikes in your traffic or app usage and sign ups, you should focus on the growth process, and not just tactics. Therefore, before you hire an agency, ask them to explain to you the process they follow and their operating rhythm (ensure they're fast and execute strong).
So, my 2 cents here, is to do your homework before you talk with anyone and prepare a basic plan including your goals (what you want to achieve). We have written a post about it in our blog so you can take a look:
Hope I helped you a bit,
Published by: Savvas Zortikis in Q&A