Could someone make a summoning whistle?
How it would work
If you had the whistle in your hand you would type /setsummon [players name] and when you use the whistle it would send a chat message to the targeted player saying "[Summoner's name] has summoned you! Type /acceptsummon to go to them." and if the targeted player typed /acceptsummon they would be teleported to the player that summoned them.