The ornamental design for a necktieextender, as shown and described.
FIG. 1 is front view of the necktie extender attached to a necktie;
FIG. 2 is a front view of the present invention; and,
FIG. 3 is a side view of the present invention.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.