We present 22 new transit observations of the exoplanets WASP-18Ab , WASP-19b , and WASP-77Ab , from the Transit Monitoring in the South ( TraMoS ) project . We simultaneously model our newly collected transit light curves with archival photometry and radial velocity data , to obtain refined physical and orbital parameters . We include TESS light curves of the three exoplanets to perform an extended analysis of the variations in their transit mid-time ( TTV ) and to refine their planetary orbital ephemeris . We did not find significant TTV _ { RMS } variations larger than 47 , 65 , and 86 seconds for WASP-18Ab , WASP-19b , and WASP-77Ab , respectively . Dynamical simulations were carried out to constrain the masses of a possible perturber . The observed RMS could be produced by a perturber body with an upper limit mass of 9 , 2.5 , 11 and 4 ~ { } M _ { \oplus } in 1:2 , 1:3 , 2:1 , and 3:1 resonances in the WASP-18Ab system . In the case of WASP-19b , companions with masses up to 0.26 , 0.65 , 1 and 2.8 ~ { } M _ { \oplus } , in 1:2 , 2:1 , 3:1 , and 5:3 resonances , produce the RMS . And for the WASP-77Ab system , a planet with mass between 1.5 - 9 ~ { } M _ { \oplus } in 1:2 , 1:3 , 2:1 , 2:3 , 3:1 , 3:5 , 5:3 resonances . Comparing our results with RV variations , we discard massive companions with 350 ~ { } M _ { \oplus } in 17:5 resonance for WASP-18Ab , 95 ~ { } M _ { \oplus } in 4:1 resonance for WASP-19b and 105 ~ { } M _ { \oplus } in 5:2 resonance for WASP-77Ab . Finally , using a Lomb-Scargle period search we find no evidence of a periodic trend on our TTV data for the three exoplanets .