If you don't have a friend to play with you can do it yourself for the Partners in Crime trophy. Just create another account and add each other friend. Create a contract on the other account and play it on your main account. You can also get the Contender trophy with this method.
Damn why did i not read it sooner i did the pitcher on the first mission and it wont give me the trophie delete data and start again. And when i was so pissed i forget about the 100 challenges trophie, i was 12 away of getting it and now i need to start that over again. Tip one read first for problems.
Great guide , helped me a lot getting the PLATINUM
Platinum Trophies : Assassin's Creed II , Uncharted 3 , Just Cause 2 , Sonic's Ultimate Genesis Collection , Mafia II , Cabela's Dangerous Hunts 2011 , Far Cry 3 , Sleeping Dogs , Dishonored , Need For Speed The Run , Hitman Absolution.