Yes, but probably not as much as you could on an omnivorous diet. It’s difficult to consume adequate amounts of complete proteins on a vegetarian or vegan diet, especially when it comes to building muscle. As a vegetarian concerned with building muscle mass, it’s worth considering adding either dairy or fish to your diet depending on your personal beliefs. A strict vegan dieter may want to focus on eating plenty of nuts, beans, and soy-based proteins to get in enough protein to aid in muscle building.
As far as vegan/vegetarian-friendly protein supplements go, rice, hemp, and soy protein powders are all good choices. A vegan diet may not be optimal for gaining muscle but it’s not impossible!
Campbell, W. W., Barton Jr, M. L., Cyr-Campbell, D., Davey, S. L., Beard, J. L., Parise, G., & Evans, W. J. (1999). Effects of an omnivorous diet compared with a lactoovovegetarian diet on resistance-training-induced changes in body composition and skeletal muscle in older men–. The American Journal of Clinical Nutrition, 70(6), 1032-1039.