No, mass as a verb means to gather or mobilize people; usually troops, or to assemble.

What are the sources of terrorism and who will attack us? Why has all that massed hard left soldiers mobilized?

A crowd of over a hundred outside your house may be on your side at this point.

What are some possible synonyms for “crowded”?

The train was more packed/crammed/cramped than usual.

What is wrong with a “really good” book about a dog?