Animal products contain what is known as complete proteins. What this means is that they have all the different amino acids that make up protein, all of which the body needs, and, critically,
all the amino acids in meat tend to be in a good balance proportional to the body's needs.
Plant foods also have all the amino acids, but often not in well balanced quantities in a single food. This means that on a vegan diet you need to
either
A Eat some legumes such as soy, lentils, beans, peas etc. Because 1 - Some of the legumes tend to have complete proteins - i.e. amino acid balance nearly as good as meat. 2 - Legumes tend to contain lysine, which is the only amino acid that is at particular risk of being low on a vegan diet.
Or
B Eat a wide variety of different plant foods and make sure you get some sources of lysine.
Years ago it was thought you needed to combine different sorts of foods at the same meal to get complete proteins, but now consensus is that you don't, as long as you get all the amino acids it doesn't matter if some are at lunch, some are at dinner, and some are a day or two later.
To sumarise all of this post in one sentence.
Get enough lysine and you'll be fine.
Per serving, legumes and seitan are the foods highest in the amino acid lysine. Tofu, tempeh, soy meats, lentils, and seitan are the highest, followed by other legume foods. Quinoa, amaranth, pistachios, and pumpkin seeds are also decent sources of lysine. Source:
http://www.veganhealth.org/articles/protein#lys
There are probably specific body building vegan forums or blogs or articles if you look for it.