A 17-year-old boy arrested as part of an investigation into Twitter messages sent to the diver Tom Daley after he and team-mate Pete Waterfield missed out on a medal on Monday has been issued with a harassment warning.

Dorset police say the teenager was bailed pending an investigation into other communications on his Twitter account.

The teenager was held at a guesthouse in Weymouth, Dorset, hours after Daley retweeted messages he had been sent soon after finishing fourth in the 10m men's synchronised platform diving event. Daley, 18, retweeted a message that said: "You let your dad down i hope you know that." The diver added: "After giving it my all … you get idiots sending me this …"

Daley's father, Rob, died from cancer last year.

A spokesman for Dorset police said: "The 17-year-old arrested in the Weymouth area this morning on suspicion of malicious communication has been issued with a harassment warning.

Speaking before the Olympics, Daley told the BBC: "Winning a medal would make all the struggles that I've had worthwhile. It's been my dream since a very young age to compete at an Olympics. I'm doing it for myself and my dad. It was both our dreams from a very young age. I always wanted to do it and Dad was so supportive of everything. It would make it extra special to do it for him."

Some later Twitter comments appear to have been removed from the site but apparent attempts by the user to apologise remained. "@TomDaley1994 I'm sorry mate i just wanted you to win cause its the olympics I'm just annoyed we didn't win I'm sorry tom accept my apology." He added: "please i don't want to be hated I'm just sorry you didn't win i was rooting for you pal to do britain all proud just so upset."

Later, however, another tweet to Daley read: "i'm going to find you and i'm going to drown you in the pool you cocky twat your a nobody people like you make me sick".

Tweets to other users who criticised his earlier message were spiked with profanity. One read: "i dont give a shit bruv i'm gonna drown him and i'm gonna shoot you he failed why you suporting him you cunt." Another, to a different Twitter user, read: "do you want me to come to your fucking house now with a rope and strangle you with it."

Duncan Goodhew, a gold and bronze medallist in swimming at the Moscow Olympics in 1980, told ITV's Daybreak: "It is appalling that people behave that way. Becky Adlington, in fact, suffered probably far worse abuse, as well, if you remember the kerfuffle some years ago.

"I suppose that social media in one sense is fantastic, but turned the wrong way round it is very, very personal and it destroys people's lives. So I think people should be much more careful about what they say."