  Co-orbital bodies are the byproduct of planet formation and evolution, as we
know from the Solar System. Although planet-size co-orbitals do not exists in
our planetary system, dynamical studies show that they can remain stable for
long periods of time in the gravitational well of massive planets. Should they
exist, their detection is feasible with the current instrumentation. In this
paper, we present new ground-based observations searching for these bodies
co-orbiting with nine close-in (P<5 days) planets, using different observing
techniques. The combination of all of them allows us to restrict the parameter
space of any possible trojan in the system. We use multi-technique observations
(radial velocity, precision photometry and transit timing variations), both
newly acquired in the context of the TROY project and publicly available, to
constrain the presence of planet-size trojans in the Lagrangian points of nine
known exoplanets. We find no clear evidence of trojans in these nine systems
through any of the techniques used down to the precision of the observations.
However, this allows us to constrain the presence of any potential trojan in
the system, specially in the trojan mass/radius versus libration amplitude
plane. In particular, we can set upper mass limits in the super-Earth mass
regime for six of the studied systems.
