The growth of the IMRO was phenomenal, particularly after Gruev settled in Salonica during the years 1895-1897, in the quality of an Exarchist school inspector. Gruev now became the soul and body of the Central revolutionary committee. Under the direction of the latter they began to issue a secret revolutionary paper, introduced ciphers (secret writing), used pseudonyms or a nom de plume, established channels for secret communication among the various local committees and also abroad-Bulgaria. A representative of the Central Revolutionary Committee was to be sent to Sofia to take charge of purchasing and dispatching, through secret channels, the necessary war provisions for the IMRO.
Gruev’s roaming from village to village , and from one city to another, resulted in a systematic revolutionary organization throughout the Province of Macedonia and the Vilayet of Adrianople. Unfortunately, for purely political reasons and in order to safeguard itself from complications, the Exarchy decided to dismiss Gruev in 1898. Soon after his dismissal Gruev moved to Monastir and there, with the cooperation of Slaveico Arsov, Paskov, and others, he began to issue another paper, secretly, of course. Sunday schools were begun, money was collected through a special "revolutionary tax", and a quantity of war materials was purchased . Gruev was again appointed to the teaching staff now in the city of Monastir, and as such, he also assumed the management of the revolutionary movement in the Vilayet of Monastir, while the active persons at the Committee in Salonica were Dr.Christo Tatarchev, Pere Toshev, and Christo Matov.
The result of Gruev’s activities in the Monastir district was felt by the Turkish authorities. The numerous chetas (bands) which infested the mountains began to terrorize the tyrannical Turkish malefactors. Gruev, being suspected as a major factor in fostering this movement, was , as a consequence, arrested on August 6, 1900. He was held in the Monastir jail until May 1902. However, this confinement did not check his revolutionary work. By means of secret writings, ciphers, etc., he was in constant touch with the various local revolutionary committees, and from the prison he was able to direct the affairs of the revolutionary district of Monastir.