Systems of classical continuous particles in the grand canonical ensemble interacting through purely attractive, yet stable, interactions are defined. By a lattice approximation, FKG ferromagnetic inequalities are shown to hold for such particle systems. Using these inequalities, a construction of the infinite volume measures is given by a monotonicity and upper bound argument. Invariance under Euclidean transformations is proven for the infinite volume measures. The construction works for arbitrary activity and temperature and for integrable long range interactions. Also, inhomogeneous systems of particles with different "charge" can be treated.