A Special Investigation Team (SIT) of the Prohibition and Excise department had summoned a dozen personalities from the Telugu film industry or Tollywood, for questioning in connection with the case.
Some of them have already appeared before the investigators, while Navdeep is scheduled to appear tomorrow, said the SIT officials.
The SIT had issued notices to all of them under the Narcotic Drugs and Psychotropic Substances (NDPS) Act after the racket, involved in supplying high-end drugs such as LSD and MDMA in and around Hyderabad, was busted on July 2.
As part of the ongoing probe, the SIT sleuths are also questioning Tollywood personalities to find out if they had any links with those arrested in connection with the racket.
The investigators yesterday grilled actor Tarun Kumar for over 13 hours. They said the actor gave them some information. "His (Kumar's) blood, hair and nail samples were also collected," they added.
Since July 19, the SIT has questioned noted filmmaker Puri Jagannadh, cinematographer Shyam K Naidu and character actor P Subba Raju, besides Tarun.
The SIT officials have maintained that the Tollywood personalities quizzed so far in connection with the case have cooperated with the investigators and given "useful" information related to the racket.
The names of some Tollywood personalities came out during the interrogation of those arrested till now.
The SIT was quizzing them to find out if they had any links with the racket as consumers or suppliers or with those arrested, Excise officials had said.
The SIT has arrested 15 people, including US citizen Dundu Anish, a former aerospace engineer who has worked with the NASA, and seven B.Tech degree-holders employed with multi-national companies in Hyderabad.
The racket was involved in supplying high-end drugs such as lysergic acid diethylamide (LSD) and methylenedioxymethamphetamine (MDMA) and the investigators suspect that film personalities, employees of MNCs and college students were among its clients.
Orders used to be placed through the 'Darknet' (a restricted online network frequently used in illegal activities) and the drugs were delivered by couriers, including from overseas, the officials had said.
Excise Minister T Padma Rao Goud had yesterday said the security of Excise Enforcement Director Akun Sabharwal would be beefed up, if needed, in view of "threat" calls to him.
The minister said after notices were issued to the film personalities, the investigation had been transparent and rejected suggestions that the film industry was being targeted.
"The government is taking all measures to make Hyderabad a drugs-free city," Mr Goud had said, adding that his department had so far seized as many as 3,000 units of LSD, MDMA, cocaine and other narcotics.
Chief Minister K Chandrasekhar Rao, on Sunday last, had directed the officials to do their job without any fear of political interference and apprehend everyone linked to the racket.