  We report twelve new transit observations of the exoplanet WASP-4b from the
Transit Monitoring in the South Project (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 +- 0.022 Rjup 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 seconds over a 4-year time span. This lack of TTVs rules out the presence of
additional planets in the system with masses larger than about 2.5 M_earth, 2.0
M_earth, and 1.0 M_earth 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 days.
