To reconnoiter is to gain information about something in a secretive manner, or in other words to do reconnaissance. It is a military term and used when spying on an enemy, usually to aid in planning an attack.
It comes from an obsolete French word which mean to recognize. And because it is French it has an alternate spelling of reconnoitre, which is the preferred spelling outside the United States. The spelling variation extends to all its forms including: reconnoitered, reconnoitred, reconnoitering, and reconnoitring.
A reconnoiterer is someone who engages in reconnaissance. There can be mulitple reconnoiterers though it is much easier to say spies.
A few hours of sunshine yesterday gave the German aviators their first opportunity in a week to reconnoiter the Russian lines. [The Spokesman Review]
Lt. Lorance was informed by pilots who reconnoitered the area that motorcycle-mounted Taliban terrorists were active in the vicinity. [Frontpage Magazine]
They were the first team to visit the county to reconnoitre the two stages from Leeds to Harrogate and York to Sheffield, and were rewarded with a victory for sprint superstar Marcel Kittel on day one. [Yorkshire Post]
His hotel room was full of grenades and uniforms, and he had command of a band of Free French fighters who reconnoitred the approach to Paris and provided information to the Allied armies. [BBC]
I wondered if Updike thought of me as a wandering reconnoiterer from the New York Jewish intellectual set to which he felt somewhat alien. [The Daily Beast]