Multithread Make in multicore server

I'm trying to do a "make buildworld" to build some jails on a Dell R710 server. 

It has 16 cores: 

[root_at_mrefns09 ~]# sysctl hw.ncpu 
hw.ncpu: 16 

but, when doing running the "make buildworld" command: 

last pid: 77993; load averages: 1.07, 1.03, 0.95 up 38+01:12:10 17:42:09 
87 processes: 2 running, 85 sleeping 
CPU 0: 1.9% user, 0.0% nice, 2.6% system, 0.0% interrupt, 95.5% idle 
CPU 1: 0.0% user, 0.0% nice, 0.4% system, 0.0% interrupt, 99.6% idle 
CPU 2: 1.9% user, 0.0% nice, 2.3% system, 0.0% interrupt, 95.9% idle 
CPU 3: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 4: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 5: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 6: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 7: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 8: 90.6% user, 0.0% nice, 5.6% system, 0.0% interrupt, 3.8% idle 
CPU 9: 0.4% user, 0.0% nice, 0.4% system, 0.0% interrupt, 99.3% idle 
CPU 10: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 11: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 12: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 13: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 14: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
CPU 15: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle 
Mem: 159M Active, 6514M Inact, 782M Wired, 126M Cache, 827M Buf, 324M Free 
Swap: 8192M Total, 44K Used, 8192M Free 

I see that there's no multithreading when running make.. is there a way to enable multiprocessing when running make? 

Many thanks, 

Kevin