I just got the same hook up message.  I haven't been on any questionable websites or subscribed to anything so I am not sure how this individual got my cell number.

I got same massage justhookup massage
I don't know who they are ?and where did they take my number ?

Just got the same "justhookup" message.

received text: "Hey its sarah i just put pics on my profile here www.justhook1up.com my username is sarahxoxo1 u might have to make a free account to view them", don't know how they got my number