We report 12 new transit observations of the exoplanet WASP-4b from the Transit Monitoring in the South (TraMoS) project. These transits are combined with all previously published transit data for this planet to provide an improved radius measurement of Rp = 1.395 ± 0.022Rjup and improved transit ephemerides. In a new homogeneous analysis in search for transit timing variations (TTVs) we find no evidence of those with rms amplitudes larger than 20 s over a 4-yr time span. This lack of TTVs rules out the presence of additional planets in the system with masses larger than about 2.5, 2.0 and 1.0 M⊕ around the 1:2, 5:3 and 2:1 orbital resonances. Our search for the variation of other parameters, such as orbital inclination and transit depth, also yields negative results over the total time span of the transit observations. Finally, we perform a simple study of stellar spots configurations of the system and conclude that the star rotational period is about 34 d.