I have the stellar and planet mass, planet velocity, radial velocity of star, stellar semimajor axis.
How should I go about to find the radius of this exoplanet?
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In general, you can't. The spectroscopy tells you about the properties of the star and the properties of the orbit and gives some information about the mass of the planet ($M \sin i$, where $i$ is the orbital inclination).
If the spectroscopy were super-precise and with extremely high signal-to-noise and high time resolution, then you might be able to map the Rossiter-McLaughlin effect with such precision that you can estimate the planet radius. However, this would only work if the planet is transiting in front of the parent star - in which case you might as well have used transit photometry in the first place.
Another possibility is to search in the spectra for the Doppler-shifted scattered starlight from the planetary atmosphere (e.g. Martins et al. 2015). However the amplitude of this is tiny depends on both the radius of the planet and its albedo/atmospheric composition.