Doctor en Ciencias, Mención Astronomía / Observing the changes in the orbital period of transiting exoplanets produced by gravitational perturbations allows to detect unseen orbital companions in the system. With this technique,known asTransitTimingVariations(TTVs),itispossibletodetectperturbers down to Earth-like masses, overcoming the limits of current Radial Velocity searches. This PhDthesishasled to along termproject: TransitMonitoringin theSouth(TraMoS)project, which consists in a methodical and homogeneous monitoring of transiting exoplanets observable from the Southern Hemisphere with the goal of searching for orbital companions, and potentially finding Earth-mass planets. Aditionally, the cumulative light curves provide improvedvalues of thephysicalparameters of theplanets, such as orbitalinclination and radius, and from those absolute mass and mean planetary density, which are critical to our model understanding of thephysics of exoplanetary interiors and their evolution. Also, establishing thepresence orabsence of otherplanetashelpsdeterminethe architecture of multi-planetary systems, and therefore is key to discriminate between different models of formation and evolution of exoplanets. In thisThesisIpresent the observations and analysis of29 transits of4 exoplanets: OGLETR-111b, WASP-5b, WASP-4b and WASP-7b. Based on the analysis of the light curves of these exoplanets we refined the ephemeris and physical parameters of all these exoplanets. Based on the temporal analysis, we found no evidence of the presence of additional planets with masses larger than ∼10 Min those systems. We place strong limits in the mass of ~10 M⊕possible perturbers especially in the orbital resonances with the transiting planets. These results support the formation theories that predict a paucity of planetary companions to Jupiter-like planets.