For anyone interested, this is the solution(I came up with) using loops as @ChrisRackauckas suggested. Thank you.
function parametrized_strogatz(du,u,p,t)
#Coupling constant
K=p["K"]
##centroid
du[1]=0
for i in 1:p["N"]
du[1]+=du[i+1]
end
du[1]=du[1]/p["N"]
#oscillators
for i in 1:p["N"]
du[i+1]=(1.0-abs2(u[i+1])+p["w$(i+1)"]*im)u[i+1]+K*(u[1]-u[i+1])
end
end