Young stars close to the sun (within 100 pc) yield an interesting sample in many respects: They are relatively bright and because of their close distance we can resolve the surroundings of these stars by using adaptive optics on 8 to 10 m class telescopes (e.g. VLT or Keck). In the K-band the achievable angular resolution is about 50 mas which corresponds to 5 AU at a star closer than 100 pc; 5 AU is about the distance between the Sun and Jupiter. This possibility can be used to study surrounding material such as disks made up of gas and dust as well as stellar and substellar companions. A sample consisting of young stars in the solar vicinity and in an evolutionary stage between the classical T Tauri phase with a disk and the zero-age main sequence can be provided by the catalog of flare stars and related objects compiled by Gershberg et al. (1999) because young stars are often variable and exhibit large eruptions (flares). In a first step we need to verify that these stars are indeed young and did not come to lie above the main sequence in a Hertzsprung-Russell diagram because they are old or unresolved binaries or multiples. Therefore, we have taken spectra of 223 stars lying above the main sequence (of the 463 stars of the sample). The distances to these stars were measured (in most cases by Hipparcos) and they are located at a few to 100 pc. The goal was to detect lithium absorption at 6708 A which all young stars have in common. In addition to the detection of lithium, we want to identify other age indicators such as filling in or emission of the Halpha -, the magnesium Ib- and the calcium lines. The G- and K-type stars of the northern hemisphere were also observed with high resolution, and high signal-to-noise ratio spectroscopy to study these objects with methods of spectral synthesis analysis to determine the surface gravity, the chemical composition, and the temperature. The age determination of these 223 stars lead to a value between 10 Myr and the zero-age main sequence, they are indeed nearby and 17 stars are clearly pre-main sequence. In the course of this work, we discovered the closest pre-main sequence star (HIP 108405 A, 10+-10 Myrs at a distance of 16.1pc). The star is younger than GJ 182 (27 pc, 20+-10 Myrs) which held the record up to now. A planet with a mass of 5 MJup in orbit of a (for this sample) typical M-star, would have an apparent magnitude in the K-band of 14.5 to 17.5 mag at a distance of 16 pc. This would lead to a magnitude difference DeltaK of 8 to 11 mag between the star and the companion, which could be detected with 8 to 10 m class telescopes at a separation of 1" or a projected separation of 16 AU. All newly discovered young flare stars were imaged using NAOS/CONICA to search for distant companions. Depending on the space motion of the stars, they have to be reobserved in one or more years to distinguish comoving companions from stagnant background stars. In this work we have measured radial velocity variations of young stars for the first time using the échelle spectrograph of the Thüringer Landessternwarte. In these measurements one can see the problems of such an investigation, such as variability caused by activity and stellar spots. But one can also see that it is in principle possible to detect planets around active young stars. To verify the results and to measure longer rotation periods, we have to observe these stars for another season.