Latvia will search for the An-2 plane in its area of responsibility, Captain Lieutenant Antanas Brencius of Lithuania's Armed Forces told the BNS newswire.
The Lithuanian Navy's Maritime Rescue Coordination Center on Sunday asked their Latvian colleagues to help find the plane, which is owned by a Klaipeda-based company.
"We asked for help because the rescue area crossed he boundaries of the Latvian Maritime Rescue Coordination Center. Also, the wind is strengthening and the search area is expanding by a nautical mile every hour," Brencius said.
Lithuania is not seeking assistance from other countries, at least for now.
A Lithuanian Air Force L 410 plane has also joined the search operation.
The single-engine civil plane An-2 had two pilots from Klaipeda and no passengers on board.
Viktoras Sisniauskas, director of Klaipedos Avialinijos, a Klaipeda-based company that provides flying services to parachute jumpers, as well as aerial fertilizer spreading and filming and photography services, told BNS that the Polish-built plane, which has room for up to 12 passengers, had been purchased in Sweden
"The plane was in a good condition. We intended to use it for our needs," he said.
According to Sisniauskas, about an hour and a half into their previous flight from Denmark to Gothenburg, Adolfas Maciulis and Alvydas Selmistraitis, both over 60 years of age and with more than 15,000 hours of flight experience, said that there were no problems.
"This is the first such case that a civil plane has gone missing when flying over the Baltic Sea," he said.
An Air Force helicopter MI-8 took off for the search on Sunday morning, but later returned to its base in Nemirseta.
According to the Lithuanian National Defense Ministry, the Aeronautical Rescue Coordination Center informed the Lithuanian Navy's Maritime Rescue Coordination Center at around 6 p.m. on Saturday that it had lost contact with an An-2 plane flying over the Baltic Sea.
The search continued throughout Sunday despite difficult weather conditions but ended shortly before 9pm without result.
Consequently the cause of the crash remains a matter of speculation.