That Wikipedia lists the following coordinates: 2°56′18″S 40°12′45″E and that link gives the decimal values as
-2.938333, 40.2125. Typing "2.938333S, 40.2125E" into google maps does take me (just barely) off the coast of Ngomeni, Kenya, but images just shows blue water, no converted oil drilling platform.
Is this a portable platform that's moored somewhere else? Are the coordinates incorrect? Has it been taken away for good? Are google maps images just old and it really is at these coordinates? Something else?
The San Marco launch platform complex was in use from March 1964 to March 1988, with a total of 27 launches, primarily sounding rockets including the Nike Apache, Nike Tomahawk, Arcas and Black Brant launchers. Low payload weight orbital launches were also made, using the solid-propellant Scout rocket (in its B, D and G subvariants). The first satellite specifically for X-ray astronomy, Uhuru, was launched from San Marco on a Scout B rocket on 12 December 1970.
The ground station is in use and continues to track NASA, ESA and Italian satellites. However, the two platforms fell into disrepair during the 1990s. Recently, the Italian Space Agency has conducted a feasibility study to reactivate it for the Russian launcher START-1.